U.S. patent number 6,449,082 [Application Number 09/956,341] was granted by the patent office on 2002-09-10 for busbars for electrically powered cells.
This patent grant is currently assigned to Donnelly Corporation. Invention is credited to Anoop Agrawal, John Cronin, Matthew Denesuk, Steve Kennedy, Robert LeCompte, Kevin McCarthy, Gimtong Teowee, Juan Carlos Lopez Tonazzi.
United States Patent |
6,449,082 |
Agrawal , et al. |
September 10, 2002 |
**Please see images for:
( Certificate of Correction ) ** |
Busbars for electrically powered cells
Abstract
Edge busbars on a substantial perimeter of an electrochromic
device are disclosed having electrical paths wrapping over the
perimeter edge. Internal busbars interior from the perimeter are
disclosed which lower the conductivity of the conductive layer of
an electrochromic device. Signals supplied to the busbars to
control the electrochromic device are controlled by a switching
power supply that allows the maintaining of the color of the
electrochromic device without application of continuous power.
Inventors: |
Agrawal; Anoop (Tucson, AZ),
Tonazzi; Juan Carlos Lopez (Tucson, AZ), LeCompte;
Robert (Tucson, AZ), Cronin; John (Tucson, AZ),
Kennedy; Steve (Tucson, AZ), McCarthy; Kevin (Tucson,
AZ), Denesuk; Matthew (Tucson, AZ), Teowee; Gimtong
(Tucson, AZ) |
Assignee: |
Donnelly Corporation (Holland,
MI)
|
Family
ID: |
26784223 |
Appl.
No.: |
09/956,341 |
Filed: |
September 20, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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347807 |
Jul 2, 1999 |
6317248 |
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Current U.S.
Class: |
359/275;
250/214SG; 345/105; 345/49; 359/245; 359/273 |
Current CPC
Class: |
G02F
1/155 (20130101); H01M 14/005 (20130101); H05K
3/403 (20130101); H01R 12/7076 (20130101) |
Current International
Class: |
G02F
1/01 (20060101); G02F 1/155 (20060101); H01M
14/00 (20060101); H05K 3/40 (20060101); G02F
001/153 (); G09G 003/19 (); G09G 003/38 () |
Field of
Search: |
;359/245,273,275,267,254,271,265 ;264/1.31,1.38,1.7,1.9
;345/49,84,105,212 ;250/214SG |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0612826 |
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Aug 1994 |
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EP |
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2 268 595 |
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Jan 1994 |
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GB |
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63-106730 |
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May 1988 |
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JP |
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63-106731 |
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May 1988 |
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JP |
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4-324842 |
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Nov 1992 |
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JP |
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WO 97/38350 |
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Oct 1997 |
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WO |
|
Other References
CM. Lampert, "Electrochromic Materials and Devices for Energy
Efficient Windows", Solar Energy Materials, 11,1-27 (1984). .
N.R. Lynam, "Electrochromic Automotive Day/Night Mirrors", SAE
Technical Paper Series, 870636 (1987). .
N.R. Lynam and A. Agrawal in "Automotive Applications of
Chromogenic Materials", Large Area Chromogenics: Materials &
Devices for Transmittance Control, Optical Engineering Press,
Bellingham, Washington, pp. 46-84 (1989). .
N. Basturk and J. Grupp in "Liquid Crystal Guest-Host Devices and
Their Use as Light Shutters", Large Area Chromogenics: Materials
& Devices for Transmittance Control, Optical Engineering Press,
Bellingham, Washington, pp. 557-576 (1989). .
N.R. Lynam, "Smart Windows for Automobiles", SAE Technical Paper
Series, 900419 (1990). .
Selkowitz, S.E., Lampert C.M., Large-Area Chromogenics: Materials
and Devices for Transmittance Control, SPIE Optical Engineering
Press, Bellingham, Washington, pp. 22-45 (1990). .
Sapers, S.P., et al. in "Monolithic Solid-State Electrochromic
Coatings for Window Applications", Proceedings of the Society of
Vacuum Coaters Conference, pp. 248-255 (1996). .
Matthew, J.G.H. et al., "Large Area Electrochromics for
Architectural Applications", Journal of Non-Crystalline Solids 218,
pp. 342-346 (1997). .
Gao, J. et al., Applied Physics Letters, vol. 71, pp. 1293-1295
(1997). .
Matthew, J.G.H. et al., Proc. of 3d Symposium on Electrochromic
Materials, The Electrochemical Society, Proc. vol. 96-24,
Pennington, NJ, 1997, pp. 311-325. .
Badding, M.E., et al., Proc. of 3d Symposium on Electrochromic
Materials, The Electrochemical Society, Proc. vol. 96-24,
Pennington, NJ, 1997, pp. 369-385..
|
Primary Examiner: Ben; Loha
Attorney, Agent or Firm: Fitzpatrick, Cella, Harper &
Scinto
Parent Case Text
This application is a divisional of U.S. patent application Ser.
No. 09/347,807, filed Jul. 2, 1999, now U.S. Pat. No. 6,317,248
which claims the benefit of U.S. Provisional Application No.
60/091,678, filed Jul. 2, 1998.
Claims
What is claimed is:
1. A method to control an electrochromic device having a light
transmission property that responds to a physical or chemical
effect, wherein the light transmission property changes in response
to an electrical signal, wherein said method comprises the step of:
intermittently applying the electrical signal by controlling the on
duration t.sub.1 and the off duration t.sub.2 of the electrical
signal individually, in response to the physical or chemical
effect, effective to maintain the light transmission property
within a range of about 1% to about 10% of a predetermined value of
said light transmission property.
2. A method according to claim 1, wherein said t.sub.1 and t.sub.2
are controlled in response to the physical effect of
temperature.
3. A method according to claim 1, wherein at least one of (i) the
current, and (ii) the change of current with time, (iii) output
from photosensors, (iv) charge passed through the device, (v) cell
potential, to said electrochromic device is used to respond to the
change caused in the device by the change in temperature; by
changing said t.sub.1 and t.sub.2.
4. A method according to claim 1, wherein the temperature of the
electrochromic cell is used to influence the control circuit so as
to adjust t.sub.1 and t.sub.2.
5. An electrochromic device having a light transmission property
that responds to a physical or chemical property, wherein the light
transmission property changes in response to an electrical signal,
wherein said electrochromic device includes: a means to
intermittently apply the electrical signal by controlling the on
duration t.sub.1 and the off duration t.sub.2 of the electrical
signal individually, in response to the physical or chemical
property, effective to maintain the light transmission property
within a range of about 1% to about 10% of a predetermined value of
the light transmission property.
6. An electrochromic device according to claim 5, wherein the means
to intermittently apply the electrical signal is a control circuit
which includes: an astable timer that supplies an input to a first
RC timing circuit; and a monostable timer that supplies an input to
a second RC timing circuit; wherein a first output from the first
RC timing circuit and a second output from the second RC timing
circuit are applied to the electrochromic device.
7. An electrochromic device according to claim 6, wherein a
microcontroller provides t.sub.1 and t.sub.2.
8. An electrochromic device according to claim 5 or 6, wherein the
voltage of the electrical signal is supplied from a regulated power
supply that is regulated by a switching voltage regulator.
9. A method to control an electrochromic device having a light
transmission property that responds to a physical or chemical
property, wherein the light transmission property changes in
response to an electrical signal, wherein said method comprises the
step of: intermittently applying the electrical signal by
controlling the on duration t.sub.1 and the off duration t.sub.2 of
the electrical signal individually, in response to the physical or
chemical property, effective to maintain the light transmission
property within a range of about 1% to about 10% of a predetermined
value of said light transmission property; wherein the voltage of
the applied electrical signal is supplied from a regulated power
supply that is regulated by a switching voltage regulator.
Description
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to busbars utilized in electrically powered
cells. In particular, this invention relates to edge and internal
busbars utilized in electrochromic devices. This invention also
relates to edge and internal busbars that can be utilized in other
electrically powered cells such as electroluminescent and
photochromic devices, thin-film batteries, and other cells that use
geometries similar to the electrochromic devices described herein.
Further, this invention relates to control circuits and methods to
control the coloration of such electrochromic devices through an
intermittent application of power.
Electrochromic (EC) devices are devices in which a change in an
electrical signal applied to the EC device results in a change in
an optical property of the EC device. Typically, the optical
property is optical transmittance, although other properties can be
affected such as, for example, optical spectral distribution or
polarization. Electrochromic devices can be used for many
applications, such as rear view automotive mirrors, windows,
sunroofs, shades or visors for automotive and mass transportation
applications, architectural windows, skylights, displays, light
filters and screens for light pipes, displays, and other
electro-optical devices.
A variety of technologies exist for producing chromogenic members.
"Chromogenic devices", as used herein, is employed as commonly
known in the art. Examples of these chromogenic devices include
electrochromic devices, photochromic devices, liquid crystal
devices, user-controllable-photochromic devices,
polymer-dispersed-liquid-crystal devices, and suspended particle
devices.
For example, electrochromic devices are discussed by N. R. Lynam
and A. Agrawal in "Automotive Applications of Chromogenic
Materials", Large Area Chromogenics: Materials & Devices for
Transmittance Control, Optical Engineering Press, Bellingham, Wash.
(1989), incorporated herein by reference. Other pertinent
references include N. R. Lynam, "Electrochromic Automotive
Day/Night Mirrors", SAE Technical Paper Series, 87036 (1987); N. R.
Lynam, "Smart Windows for Automobiles", SAE Technical Paper Series,
900419 (1990); C. M. Lampert, "Electrochromic Devices and Devices
for Energy Efficient Windows", Solar Energy Materials, 11, 1-27
(1984); JP 58-20729; and U.S. Pat. Nos. 3,521,941, 3,807,832,
4,174,152, 4,338,000, 4,652,090, 4,671,619, 4,702,566, 4,712,879,
4,793,690, 4,799,768, Re. 30,835, 5,066,112, 5,073,012, 5,076,674,
5,122,647, 5,142,407, 5,148,014, 5,239,406, and 5,657,149 each
incorporated herein by reference.
Electrochromic panels are also discussed by Sapers, S. P., et al.
in "Monolithic Solid-State Electrochromic Coatings for Window
Applications", Proceedings of the Society of Vacuum Coaters
Conference (1996), incorporated herein by reference, with regard to
devices of the type shown in FIG. 1E. Devices comparable to that
shown in FIG. 1E, and having photovoltaic layers for self-biasing
operation are also described in U.S. Pat. No. 5,377,037.
Other related references of interest include U.S. Pat. No.
5,241,411, U.K. Patent No. 2,268,595, Japanese Laid-Open Patent No.
Appln. No. 63-106730, Japanese Laid-Open Patent No. Appln. No.
63-106731, and U.S. Pat. No. 5,472,643, each incorporated herein by
reference. Also pertinent is International Application No. PCT/US
97/05791, incorporated herein by reference, which pertains to
electrochromic devices that can vary the transmission or reflection
of electromagnetic radiation by applying an electrical stimulus to
an EC device. International Application No. PCT/US 97/05791 uses a
selective ion transport layer in combination with an electrolyte
having at least one redox active material to provide a
high-performance device.
Also suitable for use in this invention are liquid crystal devices
such as those described by N. Basturk and J. Grupp in "Liquid
Crystal Guest-Host Devices and Their Use as Light Shutters", Large
Area Chromogenics: Materials & Devices for Transmittance
Control, Optical Engineering Press, Bellingham, Washington (1989),
incorporated herein by reference.
User-controllable-photochromic devices (UCPC) are discussed in U.S.
Pat. No. 5,604,626, entitled "Novel Photochromic Devices",
incorporated herein by reference.
Polymer-dispersed-liquid-crystal (PDLC) devices are described by N.
R. Lynam and A. Agrawal, "Automotive Applications of Chromogenic
Materials", Large Area Chromogenics: Materials & Devices for
Transmittance Control, Optical Engineering Press, Bellingham, Wash.
(1989), incorporated herein by reference.
Suspended particle devices are discussed in U.S. Pat. No.
4,164,365, incorporated herein by reference.
Examples of chromogenic devices that emit light are described in
Applied Physics Letters, Vol. 71, page 1293 (1997).
Examples of chromogenic devices that can store image patterns due
to a change in an optical property of a material are described in
U.S. Pat. No. 5,744,267, incorporated herein by reference.
The general control of chromogenic devices is discussed in U.S.
Pat. Nos. 4,793,690, 4,799,768, 5,007,718, and 5,424,898,
incorporated herein by reference.
The phenomenon of prolonged coloration of chromogenic devices is
discussed in U.S. Pat. Nos. 5,076,673 and 5,220,317, each
incorporated herein by reference.
FIGS. 1A through 1E depict typical examples of known electrochromic
devices, while FIG. 1F shows another known type of chromogenic
device.
For example, FIG. 1A depicts a layered EC device which includes a
substrate 101, transparent conductor 103, electrochromic (redox)
medium 105, transparent conductor 103' and substrate 101'.
FIG. 1B illustrates a layered EC device which includes a substrate
101, transparent conductor 103, EC layer 107, electrolyte (redox
medium) 109, transparent conductor 103' and substrate 101'.
FIG. 1C shows another layered EC device having a substrate 101,
transparent conductor 103, EC layer 107, ion-selective transport
layer 111, electrolyte (redox medium) 109, transparent conductor
103' and substrate 101'.
Still another such EC device is shown in FIG. 1D. This device
includes a substrate 101, transparent conductor 103, EC layer 107,
electrolyte 113, counterelectrode 115, transparent conductor 103'
and substrate 101'.
FIG. 1E shows an EC device having a substrate 101, transparent
conductor 103, EC layer 107, electrolyte (ion-conductive layer)
117, counterelectrode 115 and transparent conductor 103'.
A typical liquid crystal or PDLC device is shown in FIG. 1F. This
device includes a substrate 201, transparent conductor 203, liquid
crystal or PDLC medium 205, transparent conductor 203' and
substrate 201'.
Since the above chromogenic devices are known to those skilled in
the art, a detailed explanation of the manner of construction and
operation of such devices is not necessary.
In general, it is important to distribute the voltage to an
electrochromic (EC) device uniformly in order to (i) maintain the
uniformity of the coloration and bleaching of the EC device during
changes between such states of coloration and bleaching, (ii) to
improve uniformity in such colored and bleached states, and finally
(iii) to enhance the kinetics of coloration and bleaching. As the
size of an EC device increases, it becomes increasingly more
difficult to maintain the desirable voltage distribution uniformity
because increased size typically leads to increased resistance of
various components. Such increased resistance results in voltage
drops and current losses that adversely affects the uniformity of
voltage distribution.
In other electrical devices, a particular spatial voltage
distribution profile often is desired. As the size of such devices
increases, similar to the example of EC devices, it also becomes
increasingly more difficult to maintain the desired spatial voltage
distribution profile because of the increasing electrical
resistance of various components.
An applied voltage is commonly distributed at the periphery of EC
devices through the use of an edge busbar which distributes an
applied voltage to a surface conductor electrode. The applied
voltage causes a response in a particular responsive property of an
EC device. Consequently, spatial or temporal differences in the
applied voltage will cause spatial or temporal differences in the
responsive property. Ohmic losses along an edge busbar can
therefore critically affect the even distribution of voltage,
leading to undesirable non-uniformities in the coloration and
bleaching of an EC device.
Furthermore, EC devices often employ thin film transparent
conductors such as indium tin oxide (ITO) and doped tin oxides
(DTO) for the surface conductor electrode. Such thin film
transparent conductors are also used in a wide range of
applications in other areas such as displays, solar cells, and
liquid crystal devices. If the magnitude of the electrical currents
in such devices is large, there can be a considerable electrical
potential drop across the transparent conductor. Similar to the
effect of voltage variations along an edge busbar, variations of
voltage in thin film transparent conductors can also lead to
spatial inhomogeneities in the device behavior as well as to slower
overall device kinetics. Such effects become increasingly
noticeable and problematic with increasing device area.
Another related aspect of electrochromic devices is that they are
current consuming devices. Accordingly, it is advantageous for the
transparent conductors, i.e., the surface electrodes, to be very
conductive. For applications such as large area EC panels, where
current consumption is large, it is particularly important that the
transparent conductors possess high effective conductivities.
Present conventional large-area EC devices fabricated from
commercially available transparent conductors such as, for example,
ITO and DTO, generally possess slow kinetics and often display
nonuniform coloring. For example, large-area EC devices presently
are often darker at the edges than in the center.
EC devices can be fabricated on one substrate as described in U.S.
Pat. No. 4,712,879; J. Gordon H. Matthew et. al., Proc. of 3d
Symposium on Electrochromic Materials, The Electrochemical Society,
Proc. Volume 96-24, Pennington, N.J., 1997, p. 311; and Badding, M.
E., et al., Proc. of a 3d Symposium on Electrochromic Materials,
The Electrochemical Society, Proc. Volume 96-24, Pennington, N.J.,
1997, p. 369, each incorporated herein by reference.
Electrochromic devices can also be made using two substrates as
described in U.S. Pat. Nos. 4,761,061, 4,768,865, 4,902,108,
5,142,407, 5,231,531, 5,472,643, and U.S. patent application Ser.
No. 09/155,601, filed Aug. 9, 1997, each incorporated herein by
reference.
Prior art EC devices are also described in Lynam N. R., Agrawal,
A., Automotive Applications of Chromogenic materials, in Large-Area
Chromogenics: Materials and Devices for Transmittance Control, SPIE
Optical Engineering Press, Bellingham, Wash., 1990, p. 46 and
Lampert C. L., Selkowitz, S. E., Large-Area Chromogenics: Materials
and Devices for Transmittance Control, SPIE Optical Engineering
Press, Bellingham, Wash., 1990, p. 22, each incorporated herein by
reference.
U.S. Pat. Nos. 5,202,787 and 5,151,824, each incorporated herein by
reference, show the way busbars in an EC device are typically put
on the substrate edges in the prior art. As shown in FIGS. 2, 3A,
and 3B, taken from the referenced patents, in a commercial EC
automotive mirror which features two substrates 2223 and 2224, or
3333 and 3334, the substrates are staggered slightly with respect
to each other. Spring clips 2221 and 2222, or 3331 and 3332, of a
conductive material such as a copper sheet or a beryllium copper
coated with tin are clipped to the two staggered edges of
substrates 2223 and 2224, or 3333 and 3334, in order to provide an
electrical connection to substrates 2223 and 2224, or 3333 and
3334. The two substrates must be offset, or staggered, from each
other in order to expose surfaces 2225 and 3335 for the attachment
of clips 2221 and 2222, or 3331 and 3332. The surfaces 2225 and
3335 are minimized in order to maximize the optical throughput area
of the device--that is, to maximize the overlapping area of the two
substrates. Accordingly, the prior art provides electrical
connections at less than one half of the perimeter of each
substrate.
When a potential is applied to the wire clips 2221 and 2222, or
3331 and 3332, only a small potential drop occurs in these clips
because of their high conductivity. The small potential drop can be
neglected for small dimensions. However, as the dimensions of the
application increases, the potential drop can become significant.
Such potential drops can be a problem because the potential drop
comes at a cost to the potential available to the chromogenic
elements themselves. Further, significant current flow can occur at
the clips and clip junctions, thereby adversely adding to the
overall current load.
The resistance of a typical wire clip used in commercial automotive
mirrors that are about 12 inches (30 cm) in length is about 0.2
.OMEGA.. The conductivity associated with the clip depends on the
intrinsic conductivity of the material, the geometric parameters of
the clip (such as thickness, width and the length of the strip),
and on the relevant contact resistance.
To demonstrate the current consumption in the EC devices, a
commercial EC automotive mirror was colored by applying a DC step
voltage of 1.4V. The mirror initially consumed a current of 3
mA/cm.sup.2, decreasing to 0.9 mA/cm.sup.2 in the fully colored
state.
According to Hichwa, B.Pl, "Large Area Electrochromics for
Architectural Applications", International Conference on Coatings
on Glass, Saarbrucken, Germany, October 1996, an EC window device
made from all thin films on a single substrate when powered at 1.8V
showed an initial current consumption of about 2 mA/cm.sup.2 which
decreased to about 1 .mu.A/cm.sup.2 in the colored steady-state. By
assuming that such devices can be fabricated with the above current
values scaling with size while keeping similar performance
characteristics, the current consumption can be calculated for an
EC automotive mirror and a single substrate EC window at different
dimensions.
Table 1 shows the current consumption of the devices with two
different active areas: (1) 6 inches by 6 inches (15 cm.times.15
cm) and (2) 12 inches by 12 inches (30 cm.times.30 cm).
TABLE 1 Colored (steady Device Initial current state) current
type/Size consumption consumption Auto Mirror, 0.7 A 0.2 A 6 inch
(15 cm) Thin film 0.5 A 0.2 mA window, 6 inch (15 cm) Auto Mirror,
2.8 A 0.8 A 12 inch (30 cm) Thin film 1.9 A 0.9 mA window, 12 inch
(30 cm)
Therefore, as the size of the EC device increases, the current
loads that the electrodes must carry are substantially
increased.
Table 2 shows the resistance characteristics of several materials
and the resistance associated with a tape with a dimension of 1
meter in length, 2 mm in width and 0.1 mm in thickness. Table 2
also shows the resistance drop in these tapes when they carry 0.1,
1 and 10 A of current.
TABLE 2 Data for one m long tape with a width of 2 mm and a
thickness of 0.1 mm Resistivity Voltage drop Voltage drop Voltage
Drop at 25.degree. C. Resistance at 0.1 A at 1 A at 10 A Material
(10.sup.-8 .OMEGA.m) (.OMEGA.) (v) (v) (v) Aluminum 2.71 0.1355
0.01355 0.1355 1.355 Copper 1.71 0.0855 0.00855 0.0855 0.855 Gold
2.21 0.1105 0.01105 0.1105 1.105 Silver 1.62 0.081 0.0081 0.081
0.81 Tungsten 5.39 0.2695 0.02695 0.2695 2.695 ITO 200 10 1 10 100
Stainless steel 72 3.6 0.36 3.6 36 type 304 Tin 11.5 0.575 0.0575
0.575 5.75 Copper/beryllium (98/2) Indium 8 0.4 0.04 0.4 4 Nickel
7.12 0.356 0.0356 0.356 3.56 Rhodium 4.3 0.215 0.0215 0.215 2.15
Nichrome 150 7.5 0.75 7.5 75 Solder 16 0.8 0.08 0.8 8 (Pb/Sn,
67/33) Solder 25 1.25 0.125 1.25 12.5 (Sn/Ag, 95/5) Conductive
epoxy 300 15 1.5 15 150 Ablebond .RTM. 8380 Silver Frit 7 0.35
0.035 0.35 3.5 (Dupont, 1991)
As seen in Table 2, several materials incur serious voltage drops
across their resistance runs (for a specific geometry) for the
amount of current that must be provided to the EC cell. Since EC
devices are typically powered at 1 to 3 volts, the voltage drop can
significantly affect the actual voltage applied to the EC material,
causing increases in coloration and bleach times, and in certain
devices, leading to nonuniform coloration in the steady state
condition. The problem of the voltage drop, resulting from the
electrode resistance, is compounded by the increase in current when
the size of the device gets larger as seen previously in Table 1.
This invention is particularly useful for those EC devices where
the current consumption exceeds 0.1 A during either coloring or
bleaching processes.
When chromogenic devices are fabricated using two coated
substrates, the typical gap between the substrates is in the range
of from 10 to 1000 micrometers. As the size of the devices
increases, such as for a six inch by six inch (15 cm.times.15 cm)
device, in order to increase the charge throughput and to
distribute the charge uniformly, it is important that busbars be
applied to as much of the device perimeter as possible.
One prior art approach for a rectangular device as shown in FIG. 4,
is to offset substrates 3301 and 3302 simultaneously around two
edges of a corner to provide two exposed L-shaped surfaces 3304.
Then, busbars 3303 are attached in a conventional way.
In another prior art approach, busbars 5503 are applied on opposite
edges of exposed surface pairs 5504 by employing the geometry as
shown in FIG. 5 where the rectangular substrates 5501 and 5502 are
pivoted from each other so that the long dimension of each
rectangular substrate is parallel to the short dimension of the
other rectangular substrate.
Neither approach provides busbar coverage of a substantial
perimeter of a substrate. As used herein, "substantial perimeter"
means more than half of the perimeter of a substrate which is
covered by a continuous busbar. For larger devices such as those
bigger than about 6 inches (15 cm) in width and length, it is
especially desirable to put the busbars all around the device, in a
manner which covers a substantial perimeter of each substrate in
order to provide the applied signal to the entire chromogenic panel
evenly.
Nevertheless, as described above, as the length of the busbar run
increases, the resistance undesirably increases. As a result, the
prior art increases the thickness of the busbar material for large
devices in order to increase the conductivity/unit length of the
busbar in an attempt to maintain the desirably low resistance of
the busbar. However, a major problem with the use of conventional
busbars such as spring clips and wires for such large chromogenic
applications arises when the thickness of the busbar exceeds the
typical cell gaps. Even when the thickness of the busbar does not
exceed the cell gap, the geometries of the prior art busbars and
their placement limit the allowable increases to conductivities.
Further, there may also be a problem around substrate corners when
one continuous strip of the prior art busbar clip is used.
Another method with substantial coverage is provided all around the
periphery, by using thin conductors, as shown in U.S. Pat. No.
5,066,112. However, in this case, the conductor thickness is
limited by the gap between the substrates and its width.
Another approach is to make the two substrates dissimilar in size
so that the edges of one substrate extend from all around the
perimeter of the other substrate. In this configuration,
conventional wire clip busbars can be used on the larger substrate.
However, it is difficult to attach conventional wire clip busbars
to the smaller substrate due to the limited gap available between
the two substrates. The very close geometry could cause electrical
shorting of the two substrates at the conventional wire clip busbar
of the smaller substrate.
As noted above, in addition to the problem of voltage drops from
the edge busbar clips, if the magnitude of the electrical currents
in EC devices is large, there can be a considerable electrical
potential drop across the thin film transparent conductor, leading
to detrimentally slower overall device kinetics and spatial
inhomogeneities in the EC device behavior. Therefore, for
applications where current consumption is large, and especially
where the area of the EC devices is large (e.g., chromogenic
panels), it is particularly important that the transparent
conductors possess large effective conductivities. Large-area EC
devices fabricated from commercially available transparent
conductors such as, for example, indium tin oxide (ITO) and doped
tin oxide (DTO) generally possess slow kinetics and often display
nonuniform coloring (e.g., darker at the edges to which the busbars
are connected than in the center).
Values for the sheet resistance of commercially available
transparent conductors such as ITO and DTO are typically greater
than about 5 .OMEGA./sq (the units are also commonly written as
.OMEGA./.box-solid.) to about 15 .OMEGA./sq. Lower sheet
resistances may be obtained by increasing the thickness of the
transparent conductor, but this adversely affects the optical
properties (e.g., increased haziness and/or diminished
transmissivity) and also adds appreciably to the cost. It is
desirable to form substrates which possess appreciably lower
effective sheet resistance (can be less than 1 .OMEGA./sq) at a
cost that is attractive for applications such as those described
above.
U.S. Pat. No. 5,293,546, incorporated herein by reference,
describes a method for making a display device in which one of the
electrodes is preferably a metallic grid. Preferred line widths
were 20 micrometers with line spacings of 500 micrometers and line
heights of 0.2 to 3 micrometers. The grid is then coated by a metal
oxide (e.g., 1000 .ANG. of ITO). The invention relates to displays
in which high resolution processing equipment must be used for
depositing the grid pattern. Thus the cost is high, particularly if
large substrates such as 6 inch.times.6 inch (15 cm.times.15 cm) or
bigger are required because maintaining high precision in such a
fine grid pattern over increasing areas is costly. Further, since
these substrates must be over-coated with ITO, they are unable to
use more cost effective, mass produced transparent conductors, such
as mass produced ITO or inexpensive DTO deposited onto glass sheets
in a float line.
U.S. Pat. No. 4,768,865, incorporated herein by reference,
describes the use of a free-standing metallic grid as one of the
transparent conductors. In this invention, the metal grid
participates directly in the electrochemical reaction in the EC
cell. However, for most EC devices, it is not desirable for the
electron conductor also to participate in the reaction.
U.S. Pat. No. 5,724,176, incorporated herein by reference,
describes the use of a counterelectrode for a smart window that
contains a transparent substrate and a linear electrically
conductive material formed on a surface of the transparent
substrate. A layer of an electrochromic material is formed on the
window's surface, and a layer of an electrolyte is arranged between
the counterelectrode and the electrochromic electrode and in
contact with the layer of the electrochromic material. Various
patterns are described for the placement of the linear electrically
conductive material.
U.S. Pat. No. 5,066,111, incorporated herein by reference,
describes laminated EC devices. A metal grid on a glass substrate
is employed as one electrode and a longitudinal set of busbars,
preferably composed of a metal foil such as copper, or an
electroconductive ceramic frit deposited on glass or on the surface
of an electro-conductive film, is employed as the other electrode.
The electrochromic film is deposited over the second electrode.
Thus, the metal foil or frit conductors of the U.S. Pat. No.
5,066,111 invention are always in direct contact with either the
electrochromic coating or the electrolyte. However, such direct
contact can decrease the device lifetime because of reaction
between the coating and the electrolyte or electrochromic coating.
Moreover, if put on glass and then coated with the transparent
conductive coating (TCC), other problems can arise. Most
importantly, the TCC is usually deposited in a thickness of less
than 0.3 micrometers. In comparison, tapes or underlying frits,
etc., are typically in thicknesses of 10 to 1000 times the
thickness of TCC. Thus, vacuum methods that are typically used to
coat TCC have difficulty getting a conforming coating that
adequately covers the edges. The reference does not address the
relationship of the busbar thickness and width to the device
size.
POLYCHROMIC.TM. solid films are described in European Patent
Publication No. EP 0 612 826 A1, incorporated herein by reference.
The reference describes how polychromic solid films may be used in
electrochromic devices, particularly glazings and mirrors, whose
functional surface is substantially planar or flat or that are
curved with a convex curvature, a compound curvature, a
multi-radius curvature, a spherical curvature, an aspheric
curvature, or combinations of such curvature.
Often, a demarcation means, such as a silk-screened or otherwise
applied line of black epoxy, may be used to separate the more
curved, outboard blind-spot region from the less curved, inboard
region of such electrochromic mirrors. The demarcation means may
also include an etching of a deletion line or an otherwise
established break in the electrical continuity of the transparent
conductors used in such mirrors so that either one or both regions
may be individually or mutually addressed. Optionally, this
deletion line may itself be colored black. Thus, the outboard, more
curved region may operate independently from the inboard, less
curved region to provide an electrochromic mirror that operates in
a segmented arrangement. As described in European Patent
Publication No. EP 0 612 826 A1, upon the introduction of an
applied potential, either of such regions may color to a dimmed
intermediate reflectance level, independent of the other region,
or, if desired, both regions may operate together in tandem.
An insulating demarcation means, such as demarcation lines, dots
and/or spots, may be placed within electrochromic devices, such as
mirrors, glazings, optically attenuating contrast filters and the
like, to assist in setting out the interpane distance of the device
and to enhance overall performance, in particular the uniformity of
coloration across large area devices. Such insulating demarcation
means, constructed from, for example, epoxy coupled with glass
space beads, plastic tape or die cut from plastic tape, may be
placed onto the conductive surface of one or more substrates by
silk-screening or other suitable technique prior to assembling the
device. The insulating demarcation means may be geometrically
positioned across the panel, such as in a series of parallel,
uniformly spaced-apart lines, and may be clear, opaque, tinted, or
colorless, and appropriate combinations thereof, so as to appeal to
the automotive stylist.
As described in European Patent Publication No. EP 0 612 826 A1, a
demarcation means may be used that is conductive as well, provided
that it is of a smaller thickness than the interpane distance
and/or a layer of an insulating material, such as a non-conductive
epoxy, urethane or acrylic, is applied thereover so as to prevent
conductive surfaces from contacting one another and thus
short-circuiting the electrochromic assembly. Such conductive
demarcation means include conductive frits, such as silver frits
like the #7713 silver conductive frit available commercially from
E.I. du Pont de Nemours and Co., Wilmington, Delaware, conductive
paint or ink and/or metal films. Use of conductive demarcation
means, such as a line of the #7713 silver conductive frit, having a
width of about 0.09375" (0.238 cm) and a thickness of about 50
.mu.m, placed on the conductive surface of one of the substrates of
the electrochromic device may provide the added benefit of
enhancing electrochromic performance by reducing busbar-to-busbar
overall resistance and thus enhancing uniformity of coloration, as
well as rapidity of response, particularly over large area devices.
However, the non-conductive layers are applied in a way which does
not prevent the underlying frit lines from making contact with the
electrolyte or electrochromic layers. Thus, this frit may
potentially react, especially when coloring and bleaching
potentials are applied.
As described above, electrochromic (EC) devices are used to
reversibly vary the light transmission or reflection by application
of an electrical voltage. Applications of electrochromic devices
include windows for architectural use (windows, interior
partitions, skylights, light pipes), windows in transportation
(automobiles, trucks, planes, trains, boats, etc.), eye-wear, and
displays (including large area signage).
Electrochromic windows in buildings can provide higher energy
efficiency as compared to static transmission windows, while
increasing the user comfort by controlling illumination and
reducing glare. The same benefits can accrue for transportation
uses where the user comfort is enhanced by reducing solar heat and
glare during the day, while reducing the cooling load on the
air-conditioner. In many of these applications the EC device can be
required to be kept in a certain desired state of transmission for
long periods of time. For example, a window may be kept in a
darkened or bleached state for many hours of the day and may even
be kept in this state for many days.
Thus, it is desirable to enhance the durability of EC devices that
are used in this long single state mode, while reducing energy
consumption of the EC devices. Reducing energy consumption is
particularly useful in circumstances where solely a battery is used
to power such a device and thus, it is important to ensure that the
battery drain is minimized. Such circumstances include use in a
car, aircraft, watercraft, or eyeware. One aspect of the present
patent describes circuitry which addresses one or more of these
issues.
U.S. Pat. No. 5,148,014, incorporated herein by reference,
describes the use of a linear regulated power supply to power an EC
mirror.
U.S. Pat. No. 5,193,029, incorporated herein by reference,
describes the use of a Zener diode and transistor, which is
essentially a linear regulation, to provide voltage to an EC
mirror.
U.S. Pat. No. 5,220,317, incorporated herein by reference,
describes the use of a voltage divider consisting of series
resistors to scale down the voltage provided to EC elements.
Electrochromic devices which will benefit from this invention are
well known in the art. For example, these are described in U.S.
patent application Ser. Nos. 09/155,601 and 08/699,940, filed Apr.
9, 1997 and Aug. 20, 1996, respectively.
For those EC devices which are colored by applying a voltage, it
would be desirable not to require applying continuously the
coloring potential after the required coloration depth has been
reached. Such continued application of the coloring potential,
while promoting EC reactions, can also promote side reactions which
could have detrimental effect on the device longevity. This applies
for all EC devices which need to be maintained in a state of
coloration that is different from their natural transmission state.
The natural transmission state of an EC device is measured at
equilibrium with no applied potential and when the potential
difference between the opposing electrodes is zero.
Typically, the EC devices can be kept colored for a finite period
of time when the coloring potential is removed, i.e., the color of
the device will change towards its natural state over a period of
time. This change could occur over a wide range of time intervals,
from fast over several seconds or minutes, to as slow as extending
up to many days, depending on the device. A device where this
change is fast is said to have short "memory" and one where the
change is slow is said to possess long "memory". For example, U.S.
patent application Ser. No. 09/155,601 discloses devices with long
memories and compares them with devices that have short
memories.
It is clear that is would be advantageous to be able to maintain a
coloration setting without having to maintain an applied voltage to
electrochromic devices because circuitry that allows intermittent
adjustment of the voltage as needed to maintain a coloration
setting would lead to lower power consumption in the device.
U.S. Pat. No. 5,384,578 (to Lynam et.al.), incorporated herein by
reference, describes the use of intermittent voltages for
continuously variable mirror and windows, but does not relate to
changing the voltage-on or voltage-off periods and voltage-time
shapes under different conditions as discussed in the present
invention.
U.S. Pat. No. 4,298,970 (to Saegusa), incorporated herein by
reference, describes a technique for utilizing an intermittent
technique to drive EC displays with memory. The patent only
describes bimodal displays which have only two states, i.e.,
colored and bleached states and does not discuss devices which need
continuously variable light transmission across a continuum of
transmissive states.
U.S. Pat. No. 5,007,718, incorporated herein by reference,
describes a method of driving electrochromic elements by using a
current stabilizing circuit and a voltage stabilizing circuit in
tandem with a power supply to form a stabilized power source, and
applying a gradually increased coloring voltage and a gradually
decreased discoloring voltage to keep the current flow within
predetermined amounts.
U.S. Pat. No. 5,365,365, incorporated herein by reference,
describes an electrochromic system for controlling the color state
by determining the charge needed to obtain a set color from the
discharge potential of the system and the coloration set-point. An
integrator measures the charge passing through the system and
compares it to the charge to be transferred, which is measured by a
differential amplifier which compares a discharge potential
measured by a capacitor with a selected color set-point.
U.S. Pat. No. 5,231,531, incorporated herein by reference,
describes an electrochromic system in which a voltage generator is
connected to electrically conductive films by an electrical control
circuit. The voltage generator receives a set-point from a control
unit and generates a potential differences as a function of the
temperature of the electrolyte.
SUMMARY OF THE INVENTION
This invention is related to edge and internal busbars that lower
the overall effective resistance of electrical devices,
particularly EC devices, thereby enabling large devices to maintain
desirable electrical properties. The present invention describes
the benefits of applying the busbars of the present invention to a
substantial perimeter of an EC device, as well as the m aterials
and processes to accomplish this.
As shown later, the contact points with the conductive coatings
constituting the EC devices may be less than half of the perimeter,
but the busbar of the present invention runs continuously for more
than half of the device perimeter. The term "busbar" refers to a
conducting medium that provides a substantially uniform voltage to
all those points on the device perimeter that are connected to the
busbar. The busbar should be capable of carrying substantial
current with a voltage drop of preferably less than 1/10th of the
applied voltage, or a voltage drop less than that which causes a
perceptible change in the kinetics of the device (rate of
coloration and bleach) or in the depth of coloration.
The voltage drop should be less than that voltage drop which would
cause a perceptible change in the kinetics or coloration properties
of the device. Thus, for some particular devices, higher voltage
drops can be accommodated so long as such perceptible changes do
not occur. Generally, however, such voltage drops are less than
1/10th of the applied voltage.
The conductance of the edge busbar conductor is dependent on the
cross-section, length and the intrinsic conductivity of the busbar
material. Since the gap between the two substrates for a EC cell is
limited, the thickness of the busbar conductors must be within the
limitations imposed by the cell's size. To maximize the EC device
viewing area, the width of the conductor in the prior art is
limited as shown in FIGS. 4 and 5, where the width is limited to
the exposed areas 3304 and 5504. Typically, this width is less than
25 mm, preferably less than 10 mm, in order to maximize effective
cell area. At times, this width can be on the order of less than 2
mm. Further, for a device made by substrates that are exactly
stacked on one another and separated by a gap of 100 micrometers,
the thickness of the conductor on each substrate located between
the two substrates is typically limited to less than 50
micrometers.
The present invention teaches the use of materials and processes to
deposit busbars on a substantial portion of the device perimeter
while overcoming the geometric constraints described above. A
copper conductor which is 35 micrometers thick and 3 mm wide
exhibits a resistance drop of 0.16 .OMEGA. per meter. Accordingly,
for a device that is one meter square, a continuous conductor
around the device periphery will exhibit a drop of 0.32 .OMEGA.
from one diagonal edge to the other. For a device that will carry a
current as low as even one ampere, the drop of 0.32V at an applied
potential of about 1.5V is significant. This can result in
non-uniform coloration, slow kinetics, etc. In such devices, it is
preferable to maintain the potential drop below 1/10th of the
applied voltage or below any voltage that will cause a perceptible
change in the color uniformity of the device or a decrease in the
kinetics.
Since the current consumption of an EC device changes with time,
particularly when step potentials are used, it is preferable that
the potential drop in the busbar is kept within the limits
described above during both the switching period and also when the
steady state is reached. If other materials from Table 2 are used
instead of copper, except for silver, the resistance drop will be
even higher for the same busbar dimensions. Thus the geometry of
the busbar (such as thickness and width) of the tape will have to
be increased for best performance.
An object of the present invention is to overcome the prior art
constraints on edge busbar effective resistance arising from the
geometrical limitations of busbar length, width, and thickness. The
present invention uses specific geometry, materials and processes
to form the edge busbars.
This invention overcomes these geometrical limitations by forming a
conductive path from the electrode on a front side of a substrate
to the edges of the substrate and then extending this conductive
path on to the back of the substrate. On the edge of the device, on
the back, or on both the edge and the back, highly conductive paths
such as reinforcing conductors may be employed to lower the busbar
resistance. The conductive path from the front of the substrates to
the back could be the continuation of the same material which is
used for the transparent conductor, such as indium tin oxide, or
can be fabricated from a different material, so long as dimension
and conductivity requirements are met. That is, the conductivity
must be effective to prevent a potential drop of 10% or a potential
drop that would detrimentally affect the performance of the EC
panel, while the dimensions must be effective to allow the
substrates to maintain a close proximity to each other. Once the
conductive path is formed on the back of the substrates, the
geometrical limitations on the thickness and the width of the
busbar conductor are relieved substantially.
Accordingly, the present invention provides an edge busbar for an
electrical device, wherein the edge busbar comprises at least one
electrically conductive connector portion effective to form an
electrically conductive path from a surface of the electrical
device, wrapping around a portion of an edge, to an opposite
surface of the electrical device, and an electrically conductive
perimeter portion in electrical contact with the connector portion,
wherein the perimeter portion is peripherally on a substantial
perimeter of the electrical device.
The connector portion of the edge busbar of the present invention
can be continuous peripherally on a substantial perimeter of the
electrical device, can be continuous peripherally on an entire
perimeter of the electrical device, or can be composed of a
plurality of connector portions. That is, the connector portion can
wrap completely around an entire perimeter edge of the electrical
device, can wrap completely around a substantial perimeter portion
of the perimeter of the electrical device, or it can be a series of
smaller portions that each wrap around smaller portions of the
perimeter of the electrical device. Regardless, there is a
perimeter portion of the edge busbar of the present invention which
is peripherally on a substantial perimeter of the electrical device
and connects to the various connector portion(s) of the present
invention.
The front of a substrate is generally defined as the surface having
the conductive electrode layer thereon.
In the case of a two substrate device, the front of a substrate is
the surface facing the other substrate. In the case of a single
substrate EC device, the front of a substrate is the surface facing
the EC stack. In general, the layer of transparent conductive
material is on the front of a substrate.
Although other parameters such as the conductivity of the
transparent conductors (electron conductors), the ionic
conductivity of the electrolyte layer, and the intercalation rate
in the EC coating and other coatings if used, might also influence
the kinetic parameters of EC devices, as shown above, the
resistance of the edge busbar itself can have an important affect
on the performance of the EC device. Accordingly, it is an object
of the present invention to minimize the contribution of the edge
busbars towards slowing the EC device kinetics. The edge busbars of
the present invention may also assist in promoting a spatially
uniform rate of color change during coloring and bleaching
cycles.
In one embodiment of the present invention, an edge busbar includes
a connector portion that has a separation or separating portion.
However, the connector portion at each side of the separation is
electrically connected by the conductive electrode coating layer of
the electrical device. The separation is relatively small between
the connector portions on each side of the separation, so that
there is negligible resistance across the break. In other words,
the separation is electrically bridged by the conductive electrode
coating layer. This allows the connector portion to be effectively
continuous peripherally about the entire perimeter of the
electrical device even though separations exist in the connector
portion. Advantages to this configuration include ease of
manufacture and reduced complexity of design.
Busbars of the present invention can be advantageously used in
pairs. Another embodiment of the present invention provides an edge
busbar pair for an electrical device, each edge busbar comprising a
connector portion and a perimeter portion, wherein each connector
portion is effective to form an electrically conductive path from a
front surface of a substrate, wrapping around a portion of an edge
of the substrate, to an opposite back surface of the substrate. The
perimeter portions being in electrical contact with its respective
connector portion, and wherein each perimeter portion is
peripherally on a substantial perimeter of each respective
substrate, and wherein the front surfaces of each substrate face
each other with each substantial perimeter proximate to and
substantially opposite to the other substantial perimeter.
As discussed previously, each edge busbar of an edge busbar pair
can be continuous peripherally on a substantial perimeter of its
substrate, can be continuous peripherally on an entire perimeter of
its substrate, or can be composed of a plurality of connector
portions. It is advantageous for each edge busbar to be composed of
a plurality of connector portions. It is particularly advantageous
for each connector portion of each edge busbar to be in an
alternating relation with connector portions of the other edge
busbar. As shown later, when the connector portions are in such
alternating relation, the thickness of the busbar material can be
thicker than one half of the total gap distance between the
substrates and yet still not cause an electrical short. Further, a
sealant and/or an insulator can be added to assure against any
shorting. Nonetheless, as explained earlier, thicker busbar
material is desirable in order to maximize conductivity.
The present invention can be implemented for single substrate
devices or dual substrate devices. The edge busbars of the present
invention can be used singly as needed advantageously (as
contrasted with the prior art). However, single substrate devices
can nonetheless require a pair of edge busbars because such
devices, as described earlier and as known in the art, often are
made by forming an EC stack onto a substrate. In such cases, the EC
stack requires a pair conductive electrodes as well as the
substrate. Accordingly, both conductive electrodes have electrical
signals applied to them which would benefit from the advantages of
the edge busbars of the present invention.
In the present invention, an edge busbar is used having a portion
that can be fabricated of any convenient material with an effective
maximum thickness that can be inserted in the cell gap without
shorting from touching with the other busbar or with the opposing
conductive substrate. At the same time, the edge busbar of the
present invention provides sufficient conductivity such that a
negligible voltage drop (preferably less than one tenth of the
applied voltage) occurs in the edge busbar. Further, the edge
busbar of the present invention covers a substantial portion of the
device perimeter and can include the internal busbars of the
present invention.
The present invention also relates to the construction of
substrates, especially transparent conducting substrates, which
possess relatively large effective conductivities by the inclusion
of internal busbars.
The present invention further relates to the use of the
aforementioned substrates to construct affordable large area EC
devices that can be used for architectural applications, (e.g.
windows, partitions, skylights, diffuser panels, light pipes,
etc.), automotive (windows, sunroofs, etc.) or other transportation
(windows for planes, trains, buses, boats, etc.) applications, or
signage applications (including large area displays such as those
used at stock exchanges, airports and other such facilities).
The present invention also provides substrates which possess
appreciably lower effective sheet resistances (can be less than 1
.OMEGA./sq or .OMEGA./.box-solid.) at a cost that is attractive for
applications such as those described above.
The present invention teaches means for lowering the sheet
resistance of thin film transparent electrically conducting
assemblies for use in chromogenic devices, particularly
electrochromic (EC) devices. The present invention permits the
manufacture of EC devices which possess significantly improved
kinetics with regard to coloration and/or bleaching, even for
devices which possess relatively large active areas. The present
invention also results in devices which possess considerably
improved coloration and bleaching uniformity.
Most practical EC devices, as shown in FIG. 6, are comprised of an
"EC Assembly" 6601 which is effectively bound on either side by
electronically conducting electrodes (ECE) 6602. Generally
speaking, electrodes 6602 may be comprised of any of a variety of
electronic conducting materials. Because EC devices are generally
used to modulate light, however, at least one of the ECE 6602
should possess reasonable transparency at the wavelengths of
interest (mirrors and many displays, e.g., typically possess only
one transparent ECE; and window-type devices typically possess two
transparent ECE's). The present invention provides improved
effective conductivity of transparent ECE's in a manner readily
integrated into the device structure.
The present invention forms internal busbars by providing strips of
highly conductive material electrically connected to interior
portions of a transparent ECE. The internal busbars add regions of
increased conductivity into a transparent ECE, thereby lowering the
overall effective resistance of the transparent ECE. Such lowered
overall resistance leads to large device advantages.
The internal busbars of the present invention have increased
conductivity compared to the transparent ECE when measured along
the longitudinal direction of the conductive strips of the present
invention. That is, in a top view of the transparent ECE with an
internal busbar strip, when one compares a section of the
conductive strip having a length L and a width W with a section of
the transparent ECE also having the dimensions of W.times.L, the
conductivity of the W.times.L section of the internal busbar will
be higher than the conductance of the W.times.L section of the
transparent ECE, along either dimension L or W. Preferably the
conductivity of the conductive strip will be greater than about 2
times the conductivity of the transparent ECE, more preferably
greater than about 10 times.
The internal busbars of the present invention achieves such higher
conductance by several ways. According to one embodiment of the
present invention, materials having inherently higher
conductivities are used for the busbars. According to another
embodiment of the present invention, the busbar strips are made
thicker than the surrounding transparent ECE. Such thicker strips
can be embedded below the transparent ECE and/or into the
underlying substrate. It is important that these two--that is, the
internal busbars and the transparent ECE--are in electrical contact
with each other (continuous or spatially intermittent). One may
even use a material, to enhance or to tailor the electrical
characteristics of this electrical contact, different from that
material of the internal busbars or of the transparent ECE.
In another embodiment, the internal busbar strips are formed on a
different surface from that surface which has the transparent ECE.
Strip connecting portions connect interior portions of the
transparent ECE or device with segments of the internal busbar
strip. Such strip connecting portions can extend through the
substrate. The internal busbars of this embodiment are nonetheless
"internal" because they connect to regions of the transparent ECE
away from the periphery.
The present invention also is directed to circuitry which uses low
power. Another object of the present invention are circuits which
apply intermittent coloration power to EC devices in order to
maintain or control the EC devices' coloration while compensating
for the EC devices' inherent coloration decay without needing a
constant application of coloration power.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A, 1B, 1C, 1D, 1E, and 1F are side cross-sectional views of
a number of different prior art electrochromic, liquid crystal,
PDLC, and photochromic devices suitable for use in the present
invention.
FIG. 2 is a perspective view of a prior art arrangement of edge
busbars clips on two substrates.
FIG. 3A is an perspective exploded view of a prior art arrangement
of edge busbar clips on two substrates.
FIG. 3B is a sectional view of a prior art arrangement of edge
busbar clips on two substrates.
FIG. 4 is a perspective view of a prior art arrangement of edge
busbars clips on two substrates.
FIG. 5 is a perspective view of a prior art arrangement of edge
busbars clips on two substrates.
FIG. 6 is a schematic side view of an EC device.
FIG. 7A is a schematic sectional view of an EC device having edge
busbars of the present invention.
FIG. 7B is a schematic sectional view of an EC device having edge
busbars and conductive paths of the present invention.
FIG. 8A is a perspective view of an EC device with a substrate
having edge busbars of the present invention.
FIG. 8B is a schematic top plan view of a substrate having a
continuous conductive path of the present invention.
FIG. 8C is a schematic top plan view of a substrate having strip
conductive paths of the present invention.
FIG. 9A is a schematic side view of a pair of edge busbars of the
present invention.
FIG. 9B is a schematic side view of an adhesive multilayer strip
for the fabrication of an edge busbar of the present invention.
FIG. 9C is a plan view of an adhesive multilayer strip for the
fabrication of an edge busbar of the present invention.
FIG. 9D is a perspective partial view of a pair of edge busbars of
the present invention at a corner.
FIG. 10 is a schematic cross sectional view of a pair of edge
busbars of the present invention.
FIG. 11A is a side view of a prior art stacked substrate
arrangement.
FIG. 11B is a top view of a prior art stacked substrate
arrangement.
FIG. 12 is a schematic side sectional partial view of a prior art
stacked substrate arrangement.
FIG. 13 is a perspective view of a single substrate with a bottom
conductor applied according to an embodiment of the present
invention.
FIG. 14 is top view of a single substrate with a top conductor
applied according to an embodiment of the present invention.
FIG. 15A is a schematic sectional side view of a single substrate
with a top and bottom conductors applied according to an embodiment
of the present invention.
FIG. 15B is a schematic sectional side view of a single substrate
with a top and bottom conductors applied according to an embodiment
of the present invention.
FIG. 15C is a schematic sectional side detail view of a substrate
with a bottom conductor and signal connections according to an
embodiment of the present invention.
FIG. 16A is a schematic sectional side view of a single substrate
with embedded edge busbars according to an embodiment of the
present invention.
FIG. 16B is a schematic sectional side view of a single substrate
with embedded edge busbars according to an embodiment of the
present invention.
FIG. 17A is a top view of a substrate with a continuous conductor
busbar according to an embodiment of the present invention.
FIG. 17B is a perspective view of a substrate with a continuous
conductor busbar according to an embodiment of the present
invention at an intermediate fabrication step.
FIG. 18 is a graph of the light transmittance vs. time for
different busbar configurations according to the present
invention.
FIG. 19A is a schematic sectional view of a stacked circular
substrate arrangement according to an embodiment of the present
invention.
FIG. 19B is a top view of a stacked circular substrate arrangement
according to an embodiment of the present invention.
FIG. 20A is a schematic perspective view of a coated substrate with
internal busbars formed on the surface according to an embodiment
of the present invention.
FIG. 20B is a schematic perspective view of a coated substrate with
two sets of internal busbars formed on the surface according to an
embodiment of the present invention.
FIG. 21 is a schematic cross sectional view of a process to form
embedded internal busbars on a substrate according to an embodiment
of the present invention.
FIG. 22 is a schematic plan view of a device with internal busbars
having different widths according to an embodiment of the present
invention.
FIG. 23 is a schematic cross sectional side view of a device with
internal busbars having a transverse axis parallel to a sight line
that is at an angle to the surface normal according to an
embodiment of the present invention.
FIG. 24 is a schematic cross sectional diagram of a device
according to an embodiment of the present invention having internal
busbars that cause a property change when a signal is applied
between them, a different property change when a signal is applied
along each busbar equally, and changes in both properties when a
difference occurs in the signals applied to each busbar according
to an embodiment of the present invention.
FIG. 25A is a schematic plan view of a group of internal busbars
addressable as a group according to an embodiment of the present
invention.
FIG. 25B is a schematic plan view of a group of internal busbars
individually addressable according to an embodiment of the present
invention.
FIG. 26A is a schematic plan view of two groups of internal busbars
arranged at an angle to each other according to an embodiment of
the present invention.
FIG. 26B is a schematic plan view of a group of internal busbars
arranged substantially parallel to each other according to an
embodiment of the present invention.
FIG. 26C is a schematic plan view of a spiral internal busbar
according to an embodiment of the present invention.
FIG. 27A is a schematic plan view of a group of internal busbars
connected to the conductive layer by conductive posts according to
an embodiment of the present invention.
FIG. 27B is a schematic side sectional view of a group of internal
busbars connected to the conductive layer by conductive posts
according to an embodiment of the present invention.
FIG. 28 is a schematic perspective exploded view of a group of
internal busbars connected to the conductive layer by conductive
posts according to an embodiment of the present invention.
FIG. 29 is a schematic side sectional close up view of an internal
busbar connected to the conductive layer by a conductive post
according to an embodiment of the present invention.
FIG. 30 is a graph of the transmissivity v. elapsed time for EC
cells of different sizes without internal busbars or edge
busbars.
FIG. 31A is a schematic plan view of a set of internal busbars
disposed on a substrate according to an embodiment of the present
invention.
FIG. 31B is a schematic sectional view of a set of internal busbars
disposed between two substrates according to an embodiment of the
present invention.
FIG. 31C is a schematic sectional view of a set of internal busbars
disposed between two substrates according to an embodiment of the
present invention.
FIG. 32A is a schematic sectional view of an electrically
reinforced edge busbar according to an embodiment of the present
invention.
FIG. 32B is a schematic sectional view of an electrically
reinforced edge busbar according to an embodiment of the present
invention.
FIG. 32C is a schematic sectional view of an electrically
reinforced edge busbar according to an embodiment of the present
invention.
FIG. 32D is a schematic sectional view of an electrically
reinforced edge busbar according to an embodiment of the present
invention.
FIG. 32E is a schematic sectional view of an electrically
reinforced edge busbar according to an embodiment of the present
invention.
FIG. 33A is a plan view of an electrochromic cell according to an
embodiment of the present invention.
FIG. 33B is a cross-sectional side view of an electrochromic cell
according to an embodiment of the present invention.
FIG. 34A is a graph of the coloration kinetics of a 6" by 3" (15
cm.times.7.5 cm) electrochromic window with internal busbars
according to an embodiment of the present invention, and of a
comparison electrochromic window without internal busbars.
FIG. 34B is a graph of the current/time behavior of a 6" by 3" (15
cm.times.7.5 cm) electrochromic window with internal busbars
according to an embodiment of the present invention, and of a
comparison electrochromic window without internal busbars.
FIG. 35 is a graph of light transmission (T) and applied voltage
(V) as a function of time (t) according to an embodiment of the
present invention.
FIG. 36A is a circuit diagram of an embodiment of the present
invention that includes a thermistor.
FIG. 36B is a circuit diagram of an embodiment of the present
invention that includes a micro-controller.
FIG. 37A is a circuit diagram of a switching regulator circuit
according to an embodiment of the present invention.
FIG. 37B is a circuit diagram of a switching regulator circuit
according to an embodiment of the present invention.
FIG. 37C is a circuit diagram of a switching regulator circuit
according to an embodiment of the present invention yielding a very
low quiescent current.
FIG. 38A is a circuit diagram of a switching regulator circuit
according to an embodiment of the present invention having a
resistor placed in series with the power supply output and EC
cell.
FIG. 38B describes the various shapes that the voltage vs. time
curve can follow depending on the parameters of the control circuit
of the present invention that controls an EC cell and compared to
the prior art continuous step shape and the prior art linear ramp
shape.
FIG. 38C describes the various shapes that the voltage vs. time
curves can follow depending on the circuit resistance
parameters.
FIG. 39 is a circuit diagram illustrating the incorporation of an
op amp and thermistor in a circuit for regulating the voltage
supplied to an EC cell.
FIG. 40 is a circuit diagram illustrating the use of a thermistor
in a circuit to vary the output voltage with temperature.
FIG. 41 is a circuit diagram illustrating the use of a thermistor
in a comparator circuit.
FIG. 42 is a circuit diagram illustrating the use of a thermistor
in a comparator circuit.
FIG. 43 is a circuit diagram illustrating the use of an adjustable
voltage power supply with an EC device.
FIG. 44 is a circuit diagram illustrating the use of a sensing
resistor in series with the power output to limit the maximum
current flowing in the circuit.
FIG. 45 illustrates an electric circuit attached to an EC cell
having switches that may be used to determine t.sub.1. or t.sub.1
by measuring the voltage at the EC cell V.sub.cell and comparing
the value with V.sub.C or V.sub.B.
DETAILED DESCRIPTION OF THE INVENTION
Edge Busbars
In the present invention, a conductive path is formed from the
electrodes to the edges of the substrate. Preferably, this path is
extended on to the back of the substrate as shown in FIGS. 7A and
7B (the details of other coatings employed in the device have been
omitted). Two substrates 701 and 702 are shown attached to each
other at close proximity by cell adhesive 703. On the edge of the
device, preferably including on the back, highly conductive paths
are employed to lower the busbar resistance. FIG. 7A shows an edge
busbar 704 of the present invention which wraps around the edge of
the substrate to provide highly conductive paths on three sides of
the edge. FIG. 7B shows a conductive path 706 of the present
invention to which is attached a highly conductive perimeter
portion 705.
The conductive path 706 from the front of the substrates to the
back could be the continuation of the same material which is used
for the transparent conductor on the substrate, such as indium tin
oxide, or can be fabricated from a different material. Once the
conductive path is formed on the back of the substrates, the
geometrical limitations on the thickness and the width of the
busbar conductor are relieved substantially because the perimeter
portion can cover a larger area without concerns about thickness.
The busbar of the present invention includes the conductive path
and the perimeter portion.
Conductive path 706 forms an electrical connection from the front
to the back. Therefore, the paths can be called connector portions.
These electrical connector portions can be made using conductive
adhesives, silver frits (e.g., available from Dupont Electronic
Materials, Research Triangle Park, North Carolina or FX 33-246
available from Ferro Inc. of Santa Barbra, Calif.), solder
materials, physical vapor deposition, chemical vapor deposition,
electroless deposition of metals, metallo-organics (e.g., available
from Engelhard Electronic Materials, New Jersey) and conductive
tapes. The conductivity of these connector portions need not be as
high as the perimeter portions that connect to these connector
portions because the connector portions only have to carry the
current over a short distance, hence their actual effective
resistance is low.
These connector portions could be continuous, thereby merging with
the perimeter portion, or in strips. Either connector portion
configuration, continuous or strips, encompasses a substantial
portion of the device perimeter. FIG. 8A shows two substrates 801
and 802, separated for clarity. Substrate 802 is shown with a
continuous conductive path 803. FIG. 8B shows substrate 802,
continuous conductive path 803, and an adhesive 804. FIG. 8C shows
a substrate 802', strip conductive paths 803', and adhesive 804. In
FIG. 8C, perimeter portion 805 connects strip conductive paths
803'. Perimeter portion 805 extends to a back perimeter region (not
shown).
According to the present invention, referring to FIGS. 8B and 8C,
it is not necessary to have a width of the substrate exposed
between the sealant or adhesive 804 and the connector portion or
conductive paths 803 and 803'. Depending on the nature of the
sealant and connector portion and their bonding characteristics, a
partial or a complete overlap may exist. If the connector portion
of the present invention is used in the strip form as shown in FIG.
8C, the connector portion strips on the bottom and on the top
substrates may be offset from each other, may be stacked on top of
each other, or may have no particularly set geometric
relationship.
In a preferred configuration where the connector portion strips are
offset, the thicknesses may be increased almost to the point where
they occupy the entire gap between the substrates without shorting.
Such connector portion strips are offset effective to allow an
insulating distance between a particular connector portion strip
and any neighboring connector portion strips connected to an
opposite substrate, as well as between the particular connector
portion strip and the opposite substrate. The insulating distance
can include insulating material. The insulating material can also
be preformed on the conductive strips. In a particularly preferred
configuration, the connector portion strips from one substrate are
in an alternating relationship to the connector portion strips of
the other substrate.
The perimeter portion materials could be selected from the same
list of materials as the connector portions. However, to enhance
their conductance, materials with high conductivity could be
selected and/or the geometry (i.e., increased thickness, width,
perimeter portions etc.) may be different from the connector
portions.
Thick metallic strips and wires may also be used as perimeter
portions. The conductive path of the connector portions of the
present invention overcomes the prior art's dependence on the
busbars' specific conductivity because the present invention
provides a broad area of conductance to which the connector portion
is attached.
The devices are preferably assembled (e.g., by bonding together two
substrates) after the connector portion strips or front to back
connections are attached to each of the substrates. If
counterelectrode coatings are required in the EC device, such strip
connector portions can be formed or positioned before or after
these coatings are deposited. Further, the part of the connector
portion strips on the back of the substrates can be joined or
reinforced (such as with conductive copper tapes) with highly
conducting medium either before or after the device assembly. The
adhesive in the copper tapes may be pressure sensitive adhesive
(PSA), or may be curable later into a thermosetting material by the
application of pressure, heat, radiation, moisture, or more than
one of these methods.
As described above, and further below, the edge busbars of this
invention can be augmented ("reinforced") in conductivity. That is,
the electrical conductivity is augmented or reinforced in order to
increase the busbar electrical conductivity, by such methods as (i)
by wrapping a continuous connector from the front to the back of
the substrate, thus providing a wider conductor resulting in higher
electrical conductivity, (ii) by attaching the connector to a
conductive wire, foil, or tape positioned on the back of the
substrate so that the connector's conductivity can be augmented by
the conductance of the wire, foil, solder, frit, or tape, and (iii)
attaching a wire or conductor on the edge of the substrate to
electrically contact the connector in order to augment the
conductance of the connector.
A preferred method to form the edge busbar is to use a conductive
tape with a conductive adhesive layer that conducts through the
adhesive layer thickness. FIG. 9B shows a conductive tape 909
having a conductor 911, a conducting adhesive layer 912 and an
optional insulating layer 910. A continuous strip of such a tape is
shown in FIG. 9C. Tape 909 includes the continuous conductor or
perimeter portion 913, and fingers or connector portions 914 that
will form the contact with the transparent conductor on the front
side of the substrate. The front side, as defined previously,
refers to the substrate side that faces the other substrate of an
EC device, while the back of a substrate refers to the side,
opposite to the front side, that faces away or is farther away from
the other substrate. Tape 909 connects the front of the substrate
(facing inward) by way of connector portions 914 to perimeter
portion 913 at the back of the substrate. An edge portion 915 of
connector portion 914 lies on the edge of the substrate.
As shown in FIG. 9C, perimeter portion 913 and strip connector
portion 914 could be integrally connected, i.e., one piece of tape
of the perimeter portion is preferably aligned with the bottom edge
of the substrate, or is on the backside of the substrate. The flat
side is folded and adhered to the substrate back. For a rectangular
device with sharp corners, the tape in the corner could be folded
over the back side to form a crease without effecting the connector
portions at the front side. Since there is effectively no
limitation on the gap or tape thickness on the back side (or the
outside) of the device, the procedure of the present invention can
be used without affecting the separation distance of the
substrates. Instead of a crease on the back side, the tape can be
cut and the tape strips running at an angle to each other can be
folded on top of each other on the corners. The corners may also be
bridged by a piece of another tape, wire, solder, etc., to keep
preferably one continuous electrical path forming a perimeter
portion for each substrate. The tape or the strip on the back can
be made more conductive by reinforcing the tape with a more
conductive medium, e.g., more tape, wire, metallic strip, etc.
Accordingly, the perimeter portion can be multilayered or made from
a number of components.
In this description, the use of the above shape of the tape (i.e.
tape with connector portions or fingers extending from a continuous
perimeter portion) avoids any kinds of creases or kinks on the
front surface. Such kinks can develop as the tape traverses over
the corners of the substrate. It is readily understood that as an
edge bends to form a curve or to form a corner, an inner path which
is a certain distance from the outer edge will trace a different
distance from the outer edge. In the case of a convex curve, the
inner path will be shorter. Accordingly, a non-stretching material
will tend to crease or kink to try to accommodate the excess
material on such an inner path. The recesses between each connector
portion prevents accumulation of excess material on the front side
between the substrates.
The above description shows a tape that is easily and
advantageously used for applications where a pair of edge busbars
can be placed correspondingly opposite each other on two substrates
without physical interference or electrical shorting because of the
innovative geometry of the edge busbar pairs of the present
invention. Such geometry innovatively allows the pair of edge
busbars to nest together in an alternating relation. Such geometry
further innovatively allows each of the pair of edge busbars to be
thicker than half the gap separating the substrates on which they
cover, thereby increasing the edge busbar conductivity without
shorting to each other. Such geometry also allows edge busbars to
wrap around corners without interfering busbar material in between
the substrate separation gap.
For those EC panels that are rectangular in shape, it is
particularly at the corners that certain configurations of the
present invention are important. It is important to ensure that no
fingers are located on those areas of the tape which bend around
the sharp corners. Furthermore, the fingers are spaced such that
they do not overlap each other over the conductive substrates. Any
kinks, overlaps, or creases on the front (conductive) side can
interfere with the predetermined gap between the two substrates
and, depending on the materials employed, could also lead to
electrical shorting between the two substrates.
The tape shown in FIG. 9C can optionally have an additional row of
strip connector portions 914 (not shown) on the side of perimeter
portion 913 opposite the side with the row of strip connector
portions 914 shown. In this optional configuration, perimeter
portion 913 is affixed to the edge of the substrate and the each
opposite rows of strip connector portions 914 are affixed to
respective opposite surfaces of the substrate.
Besides for substrates with sharp corners, the geometry of the
tapes described above can be similarly employed for substrates with
circular, elliptical, or any other regular or irregular shapes. For
shapes that have a gradual change, such as a circle, the width of
the strip connector fingers and the spacing between them should be
such so that no noticeable kink is introduced on the front side of
the substrate for the reasons described above.
The electrical connections to the device are made from the
perimeter portion on the back of the substrate by using more
conductive tape, solder, adhesive, wires, etc., or preferably the
tape described above may be provided in a pre-cut size and shape
that has a connector or a connector attachment already
assembled.
As shown in FIG. 9A, it is preferable for connector portion 914 of
each tape 909 to be in an alternating relationship with the
connector portions 914 of the other tape 909 to minimize the
chances of shorting or of overlapping of fingers. As shown in FIG.
9D, a corner of substrate 901 and a corner of substrate 902 meet
without any connector portions 914 at the corners. The connector
portions 914 remain in an alternating relationship to prevent any
overlap of tape conductive material.
As shown in FIG. 9B, tape 909 employed for this purpose can be
coated or laminated with a nonconductive material insulating layer
910 on the side that is non-adhering. This will reduce the chances
for shorting of the two substrates should the fingers inadvertently
overlap or if there is a malfunction, for example, when one of the
strip fingers lifts off the surface.
In another method, highly conductive busbars are made by wrapping
the connector from the substrate front to the substrate edges and
then reinforcing the edge portion with a highly conductive
material. This is shown in FIGS. 32A and 32D. The connectors are
shown as 3205 and 3205" and the reinforcements as 3203 and 3203'"
forming the busbars 3202 and 3202'". The reinforcement can be any
convenient shape such as a cylindrical wire, as shown for example.
Another shape is a flattened wire. In this example the conductor is
shown significantly thicker at the edges than its thickness on the
front of the substrate. In FIG. 32D, the reinforcement is located
in a precut groove on the edges of the substrate.
FIG. 32E shows highly conductive reinforced busbars having the
reinforcement in a groove with the conductive connector wrapping
from the front of the substrate around the edge to the opposite
side of the substrate.
The busbars can be made by any convenient method such as, for
example, by feeding the reinforcing wire and solder (as connector)
so that both can be put in place simultaneously. Another method
could be where the wire is pre-attached, e.g., by wrapping and then
mechanically tightening around the perimeter of the substrate. The
solder is then deposited on the front and the edge thus
electrically attaching the reinforcement with the connector. In
this method it may be advantageous to have a precut groove on the
perimeter edge of the substrate in which the wire can be placed, as
shown in FIG. 32D.
The arrangement shown in FIG. 32A can be modified as shown in FIGS.
32B and 32C where the connector wraps around from the front to the
back. Similarly, the conductor shown in FIG. 32D can be extended by
having a wrap around connector (as shown in FIG. 32E). Further, the
wire may be placed in a groove on the edge (as shown in FIG. 32D)
or in a groove made in the back of the substrate close to the
perimeter edge (not shown).
The connector may be deposited by using a soldering iron, with its
tip shaped so that the solder can be melted and simultaneously
deposited on two adjacent surfaces (as shown in FIG. 32A) or on
three adjacent edges (as shown in FIG. 32B). Instead of using a
solder, a conducting adhesive may also be applied. The solder or
adhesive may be applied from a bath of molten solder or uncured
liquid adhesive by dipping the substrate edge in the bath and then
moving the part (e.g., rotationally) effective to cover a
substantial perimeter of the substrate.
To improve the reliability of the connections, it is preferred to
seal the device using a non-conducting adhesive. As shown in FIG.
10, it may even be desirable to allow the edge sealant adhesive to
fill in the remaining gap between the substrates and preferably
extend to the substrates edges for improved reliability. Substrates
1001 and 1002 are separated and attached to each other by cell
adhesive 1003. Edge busbars 1005 including conductive paths that
wrap around to the fronts of substrates 1001 and 1002 have an edge
sealant 1004 filling the respective gaps between each opposite
pairs of edge busbars. Any convenient non-conducting material can
be used such as, for example, a curable formulation such as a
caulking, a heat or radiation curable material, or a hot melt
adhesive that cures later, or a non-curable formulation such as a
hot-melt adhesive. Some examples of materials used in sealants are
silicones, polysulfides, butyls, urethanes, epoxies, vinyls,
polyolefins, polyamides and acrylics, etc. Hot melt urethanes that
cure later due to the diffusion of moisture may be preferred as a
sealant because devices so made could be handled soon after
fabrication and a non-flowable, non-sagging bond is obtained after
curing. One may preferably employ the cell adhesive 1003 to be the
same as edge sealant 1004. This adhesive may have spacers so that
the cell spacing is governed by the size of these spaces and the
thickness of edge busbars 1005. This avoids electrical shorts
between the two substrates, due to busbar peel, moisture
condensation or conductive impurity.
Although the present invention has been discussed in terms of
electrochromic devices, it can also be useful in photochromic
devices (U.S. Pat. No. 5,604,626, incorporated herein by
reference), liquid crystal based devices as described in
Motogomery, G. P., in Large-Area Chromogenics: Materials and
Devices for Transmittance Control, SPIE Optical Engineering Press,
Bellingham, Wash., 1990, p. 577, suspended particle devices
(Research Frontiers Inc., Woodbury, N.Y.) and other devices.
Highly conductive busbars may be deposited on single substrate
devices in a number of ways to achieve substantial perimeter
contact. In the prior art, for example in U.S. Pat. No. 5,187,607,
incorporated herein by reference, the busbars for an EC device do
not cover a substantial perimeter of the device. As shown in FIG.
12 (taken from U.S. Pat. No. 5,187,607) a busbar is formed on the
edges of the substrate. The first transparent coating layer (bottom
conductor) is deposited so that it touches both the busbars, but it
is not continuous. This coating is either etched or deposited in
such a way (e.g., by masking) that there is no electrical
continuity between the two busbars. The coatings which comprise the
EC stack are substantially deposited on one of these sections.
However, the top conductor is deposited in such a way that it
touches the second part of the bottom conductor and is electrically
insulated from the first part of the bottom conductor by the EC
stack. Thus, in this design none of the two busbars occupies a
substantial perimeter of the device. Instead, the busbars run along
the two edges similar to the prior art discussed previously.
As shown in FIGS. 11A, and 11B, the use of busbars according to the
present invention which are deposited on a substantial perimeter of
an electric cell can be effectively employed for those devices that
use thin coatings on one substrate. A substrate 1101 has a
transparent electrode 1102 on its front surface. An EC stack 1104
is on the transparent conductor 1102. A bottom busbar 1103 is
formed on the perimeter of the transparent conductor 1102 while a
top busbar 1105 is formed on the perimeter of the top of the EC
stack. Electric leads are connected to each busbar.
As shown in FIG. 13, a bottom electrode 1402 is formed on substrate
1405 in a pattern with recesses 1301 at the edges of bottom
electrode 1402. Bottom electrode 1402 can be formed by any
convenient method such as, for example, by depositing the bottom
electrode (e.g. made from ITO, doped tin oxide, doped zinc oxide,
etc.) over an appropriate mask, or by etching through an
appropriate mask after deposition. Preferably, the sheet resistance
of the transparent conductors is less than about 30
.OMEGA./.box-solid., more preferably less than about 15
.OMEGA./.box-solid., and most preferably less than about 10
.OMEGA./.box-solid..
The EC stack is then deposited along with the top electrode only
onto the device area, and recesses 1301 in the electrode border
area. Optionally, one can deposit the EC stack over the device area
and only the top electrode layer would extend into recesses 1301 of
the electrode border. It is important to keep the top electrode
layer and the bottom electrode layer from shorting, thus it is
desirable that the top electrode be deposited in such a way that it
covers only a portion of recesses 1301 in the border region to
avoid shorting. Optionally, an insulating layer can be
deposited.
As shown in FIGS. 14, 15A, and 15B, one embodiment includes forming
an EC stack 1406 on bottom electrode 1402. A top electrode 1401 is
formed on EC stack 1406. An edge busbar 1404 connects to top
electrode 1401, while an edge busbar 1403 connects to bottom
electrode 1402. Edge busbar 1404 comprises a perimeter portion
1404C and a connector portion 1404D. Connector portion 1404D
includes a contacting portion 1404A and an edge portion 1404B.
Contacting portion 1404A electrically contacts a surface of top
electrode 1401. Edge busbar 1403 comprises a perimeter portion
1403C and a connector portion 1403D. Connector portion 1403D
includes a contacting portion 1403A and an edge portion 1403B.
Contacting portion 1403A electrically contacts a surface of bottom
electrode 1402. Connector portion 1404D and 1403D are in
alternating relationship on each side of EC device 1444.
One method to form the continuous busbar on this device is to
utilize a tape as shown in FIGS. 9B and 9C. As described earlier,
the first tape is placed around the periphery of the device with
its fingers touching the bottom electrode in the connector border
area. The continuous body of the tape is folded and adhered to the
back of the substrate. The fingers of the tapes form the connector
portions 1403D and 1404D. The fingers of the second tape are then
adhered on the top electrode (in the connector border area) and
folded and adhered to the back of the substrate.
The tapes, after assembly, appear as shown in FIGS. 15A and 15B in
a cross-section view (two sections shown from FIG. 14). One of the
tapes is wider, in order to protrude out. Perimeter portion 1403C
extends beyond perimeter portion 1404C to expose surface 1403E.
This allows connection to be made to both edge busbars 1403 and
1404 directly to any convenient point or points on perimeter
portion 1404C and to any convenient point or points on exposed
perimeter portion 1403E.
Referring to FIG. 15C, the connection can be made by removing the
insulating layer locally, or the tape may come with a
connector-adapter and/or connector pre-attached as discussed
earlier. Connections 1408A and 1408B are shown connecting to
perimeter portions 1403C and 1404C, respectively while being
insulated from perimeter portions 1404C and 1403C, respectively.
Connections 1408A and 1408B can be, for example, a conductive wire
or tape connected to an exterior signal connector. Connections
1408A and 1408B can be attached at only one corner (a smaller
portion of the device perimeter), or at a longer portion of the
device perimeter such as, for example, a substantial perimeter.
In all cases, one must be careful that the two busbars 1403 and
1404 do not electrically short in the regions 1410 where an edge of
perimeter portion 1403C meets edge portion 1404B at the edge of
substrate 1405. Shorting can be avoided by ensuring that the
insulator layer of the tape extends out and covers the edges of the
conductor. Alternatively, after adhering the first tape, these
edges can be treated with an insulating material (tape, adhesive,
coating) before the second tape is applied.
Once all the edge busbars are in place, the edges of the EC device
1444 can be encapsulated, for example, by injection molding (e.g.,
using thermoplastic elastomers or plasticized polyvinyl chloride)
or reaction injection mold (e.g., using polyurethane) with a resin
that can be solidified to ensure the reliability of the
connections. It may even be desirable to cover the entire device
with another substrate (preferably a glass or a plastic sheet) for
mechanical and environmental protection before edge encapsulation.
This cover substrate may also incorporate UV blocking
characteristics. The edge encapsulation may be achieved such that a
connector plug (which is internally connected to the busbars) is
molded therein which can be easily disconnected from the power
supply. This will allow EC panels to be quickly serviced and
replaced in the field.
As shown in FIGS. 16A and 16B, busbars 1602 may be embedded in the
edge of a substrate 1601 or busbars 1603 may be embedded in the
edge regions of substrate 1601. The appropriate region of the
substrate is etched, ablated, or otherwise conveniently removed to
form a recess. A highly conductive material (e.g., a metal) is
deposited into the recess region. Planarization, to bring the
substrate surface and the busbars substantially to a plane, may be
necessary prior to the deposition of an additional layer or layers.
Such embedded busbars 1602 and 1603 can serve as perimeter portions
with connector portions formed (not shown) by any convenient method
such as, for example, wrapping tape around the edge to contact the
back surface and the embedded busbar, depositing conductive
material such as a frit or a coating around the edge from the
embedded busbar to the back surface, or attaching a multitude of
preformed conductive channels to the edge to contact the back
surface and the embedded busbar.
As described previously, the edge busbar of the present invention
provides sufficient conductivity such that a negligible voltage
drop (preferably less than one tenth of the applied voltage) occurs
in the edge busbar. The conductivity can be optionally reinforced
by the addition of a supplemental conductor portion as part of the
edge busbar of the present invention, as shown in FIGS. 32A, 32B,
and 32C. In a preferred embodiment, an ultrasonic solder dispenses
an appropriate soldering material on the edge of the substrate. A
highly conductive medium (e.g. a wire, conductive tape or foil,
etc.) is attached to reinforce the overall conductance around a
substantial perimeter of the substrate. It is preferable that both
the solder and the wire or strip are dispensed simultaneously to
form the edge busbar and the reinforcement at the same time.
The reinforcement bar can also be in the form of a closed loop with
a perimeter slightly smaller than that of the substrate. In this
case, after applying the edge busbar, the reinforcement is expanded
by heating and positioned around the edge making contact with the
busbar. Of necessary, it can be soldered to further improve
electrical contact. This method is particularly appropriate in the
case of cells having circular or oval substrates where the
reinforcement can be made in the form of a ring and contracted, by
cooling, uniformly around the substrate. Finally, a lead can be
soldered to the reinforcement.
Referring to FIG. 32A, an edge busbar 3202 is formed on a
peripheral surface and a substantial perimeter edge of a substrate
3201. Edge busbar 3202 includes a reinforcement portion 3203 which
can be any convenient conductor such as, for example, wire, foil,
or bead of solder. Reinforcement portion 3203 is shown as a
circular cross-sectional wire attached to the side of the edge
portion 3205 of edge busbar 3202. A connection 3204 provides an
external electrical lead to edge busbar 3202.
Referring to FIG. 32B, an edge busbar 3202' is formed on opposing
peripheral surfaces and a substantial perimeter edge of a substrate
3201. Edge busbar 3202' includes a reinforcement portion 3203'
which is shown as a circular cross-sectional wire attached to the
side of the edge portion 3205' of edge busbar 3202'. A connection
3204' provides an external electrical lead to edge busbar
3202'.
Referring to FIG. 32C, an edge busbar 3202" is formed on opposing
peripheral surfaces and a substantial perimeter edge of a substrate
3201. Edge busbar 3202" includes a reinforcement portion 3203"
which is shown as a circular cross-sectional wire attached to one
peripheral edge portion 3206 of edge busbar 3202". A connection
3204" provides an external electrical lead to edge busbar
3202".
Referring to FIG. 33A, a substrate 3301 is shown having a solder
edge busbar 3302. Solder edge busbar 3302 is in electrical contact
with one segment of a silver frit layer 3303. Another segment of
silver frit layer 3303 forms an internal busbar 3304. Internal
busbar 3304 is interior to the perimeter formed by a main epoxy
seal 3305.
Referring to FIG. 33B, two substrates 3301' and 3301", each has a
solder edge busbar 3302' and 3302" respectively. Each solder edge
busbar 3302' and 3302" are in contact with segments of silver frit
layers 3303' and 3303". A common epoxy seal 3305' bounds internal
busbars 3304' and 3304" which are segments of silver frit layers
3303' and 3303" respectively.
The Examples which follow are intended as an illustration of
certain preferred embodiments of the invention, and no limitation
of the invention is implied.
EXAMPLES
Example 1 and Comparative Examples 1C and 2C
EC devices were made having two substrates, one employing a one
half wave ITO (about 12 ohms/square) on glass substrate (from
Donnelly Applied Films, Boulder, Colo.) and the other being a TEC
15 glass (from Libby Owens Ford (LOF), Toledo, Ohio). The nominal
size of these was 6 inch by 6 inch (15 cm.times.15 cm). The gap
between the substrates was 210 micrometers. Busbars were formed
using a copper tape with conductive adhesive. Three different
configurations were made: (i) Comparative Example 1C was made in a
configuration as shown in FIG. 2, where the edge busbar was on one
edge of each substrate, (ii) Comparative Example 2C was made in a
configuration as shown in FIG. 4, where the edge busbars are on the
two edges of each substrate, and (iii) Example 1 was made in a
configuration as shown in FIG. 7A and constructed by a method as
shown in FIGS. 17A and 17B, where the edge busbars are on four
edges of each substrate. Copper tape (with conductive pressure
sensitive adhesive) was used to form the busbars. The thickness of
the copper tape was 50 micrometers and a width of 3 mm.
To form the busbar on all four edges, as shown in FIGS. 17A and
17B, four strips of copper tape 1701 were attached to substrate
1702 and then folded on the back of the substrate. Care was taken
that these strips were close but not overlapping. On only one of
the substrates, the copper tape was covered with a 50 micrometer
thick polyimide tape, the latter was wider than the copper tape by
about 1/32 of an inch (0.079 cm). This was done to prevent shorting
of the two substrates if the copper tape peeled accidentally and
touched the other substrate. optionally, tabs 1703 can be formed by
extending one portion of copper tape 1701. The two substrates were
then adhered to each other in a configuration shown in FIG. 7A. The
total gap between the two substrates was 210 micrometers
(controlled by the adhesive) and the total thickness of the tape
was 150 micrometers.
The assembled cells were powered by connecting power to the
busbars. In the case of Example 1, power was connected to one of
the copper tabs 1703 sticking out from each of the substrates. In
this example the tabs were not joined by a wire or a tape on the
back. Since the distance between the adjacent copper strips was
small, the potential drop in the intervening ITO was negligible for
this device. Thus, the busbars of Example 1 effectively formed a
continuous electrical conductor around each substrate perimeter.
The continuous electrical conductor of Example 1 included the
connector portions being effectively electrically continuous as
well as the perimeter portions being effectively electrically
continuous.
FIG. 18 shows the kinetic traces of each of the three devices when
they were colored and bleached by applying identical step
potentials. Example 1, the cell with busbar on all four sides
colors, was the fastest to color and colored the deepest (during
the time shown in the graph), while Comparative Example 1C, the one
with busbar only on one edge, was the slowest to color and also
colored the least deep of the three devices.
Example 2
An EC device 1910 was made using two TEC 15 transparent conductive
substrates as shown in FIGS. 19A and 19B. Example 2 was a circular
EC device 1910 with a substrate 1902 being 13 inches (33.02 cm) in
diameter and a second smaller substrate 1901 being 12 inch (30 cm)
in diameter. Before EC device 1910 was assembled, a busbar 1904 on
the smaller substrate 1901 was formed by screening on a silver frit
from Dupont Electronic Materials, Wilmington, Del. (frit Type
7713). The frit forming was deposited in a perimeter ring geometry
to form busbar 1904, with the outer dimensions of the ring being
substantially the same as that of substrate 1901. The width of the
ring was 2 mm and the thickness was 5.5 micrometers. In one part of
the busbar 1904 ring the silver frit was painted on the edge (while
keeping it connected to the ring) and extended on to the back of
the substrate to form a conductive path 1908 of busbar 1904 which
is conductive from the front to the back. An electrical conducting
wire 1906 is connected to conductive path 1908 on the back.
Substrate 1901 was heated to 575.degree. C. for 6 minutes to
consolidate and cure the frit. The busbar 1905 on the larger
substrate 1902 was formed by attaching a copper beryllium spring
clip 1905 around the circumference. Spring clip 1905 comprises a
continuous perimeter portion 1911 which extends circumferentially
around the edge of substrate 1902, and finger connector portions
1912 which extends radially from continuous perimeter portion 1911
to substrate 1902. A conducting wire 1907 was soldered to clip 1905
to power substrate 1902. EC cell 1910 was assembled by gluing the
two substrates together with adhesive 1903, as shown in FIGS. 19A
and 19B. The smaller substrate 1901 was kept concentric with the
larger substrate 1902.
Internal Busbars
To produce the desired improvements in EC device behavior, it is
necessary to reduce appreciably the effective resistance of the
transparent electronic conductors (TC) in the devices or to
otherwise transport charge more efficiently laterally across the
device. In contrast to the case of a TC, when the transparency of a
particular electronically conducting electrode (ECE) is not
important, the ECE can generally be made thick enough in the prior
art so that its resistance does not adversely affect the device
behavior. For example, for a prior art mirror device with an
Aluminum (Al) ECE and an ITO ECE, the Al layer can be deposited
sufficiently thick. The result, however, is that the effective
resistance of the ITO (the transparent electronic conductor or TC)
usually is the primary limiting factor which must be overcome to
improve the device behavior.
In reducing the effective resistance of a TC, it is crucial to
ensure that the means employed does not adversely affect other
components of the device operation. This is especially problematic
when the TC acts as a substrate for an active EC layer or layers
(such as for devices which contain EC tungsten oxide deposited on
ITO-coated glass substrates). In addition, one must ensure that the
means employed do not too strongly diminish the transmissivity or
apparent transmissivity of the TC or otherwise adversely affect the
cosmetics of the device. For example, the resistance of the TC may
be decreased appreciably by increasing its thickness, but increased
thickness generally has a strongly negative impact on TC
transmissivity characteristics and cost. Means for Decreasing the
Effective Resistance of The TC's
A desirable means of imparting a relatively high effective
conductivity to a TC comprises depositing a pattern of a highly
conductive material over, under, or within it (or some
combination). Commercially available TC's such as half-wave ITO or
doped tin oxide (DTO) can be used and modified by adding internal
busbars according to the present invention. As shown in FIGS. 20A
and 20B, e.g., the pattern can be formed as lines across the
substrate. These lines may or may not intersect. The lines or
patterns may be referred to as internal busbars (IB's). FIG. 20A
shows a substrate 2001 made of, for example, glass, coated with a
transparent conductive coating 2002. Internal busbars 2003 are
formed on conductive coating 2002, FIG. 20B shows additional
internal busbars 2004 transverse to internal busbars 2003.
It is important to ensure that the materials used for the internal
busbars (IB) of the present invention do not react with the cell
components. That is, the internal busbars should be chemically and
electrochemically isolated from the reactive layers of the cell.
Reactive layers are the electrolyte, the ion insertion electrodes,
and the electrochromic layers. In these layers, chemical and
physical reactions take place when the cell is colored or
bleached.
The chemical and electrochemical isolation can be by any convenient
means such as, for example, by interposing a barrier layer between
the IB and the reactive layer. The property of being not ionically
conductive is a requirement of the optical passivation layer so
that, when a voltage is applied to the finished cell for coloring
or bleaching, no ion transport takes place from any of the cell
components to the internal busbars and vice versa.
As described below and in the figures, the isolated IB's of this
invention are connected to the conductive layers by connecting
portions that are electrically conductive. Accordingly, the IB's of
this invention can provide substantial improvement of the
electrical properties of the conductive layer while not being in
contact with the layer.
A calculation of the effective sheet resistance corresponding to a
pattern consisting of parallel lines on a transparent conductor was
performed. The physical dimensions of these internal busbars (e.g.,
their thickness (or height), width, length, resistivity), along
with the underlying transparent conductor characteristics,
determine the overall effective sheet resistance. Tables 1A, 1B,
and 1C below show the calculated effective sheet resistance of the
substrates for various values of the relevant parameters. The
calculations were made for 5 cm.times.5 cm square substrates
traversed by five (n=5, or "N.sub.5 ") parallel internal busbars,
each of width w.sub.s and height h.sub.s. For these calculations,
the strips were assumed to be composed of Pt-metal
(.sigma.=0.96.times.10.sup.5 (.OMEGA.cm).sup.-1). The effective
sheet resistance was taken as the resistance that would be measured
between an electrode connected on one full side of the square and
another connected to the opposite full side. It should be noted
that the calculations can be repeated for a grid pattern which may
consist of curved lines or non-uniformly dimensioned (e.g., in
width and thickness) conductive line patterns.
TABLE 1A h.sub.s.backslash.w.sub.s w.sub.s h.sub.s 0.01 mm 0.05 mm
0.1 mm 0.15 mm 100 nm 13.29 13.448 13.396 13.344 1 .mu.m 12.526
9.721 7.595 6.232 2 .mu.m 11.683 7.595 5.283 4.051 3 .mu.m 10.946
6.232 4.051 3.001 4 .mu.m 10.297 5.283 3.284 2.383 0.1 mm 1.538
0.339 0.171 0.115
Table 1A. Calculated effective sheet resistances
.OMEGA./.box-solid. for a system comprising 3 strips, where each
strip possesses the dimensions (h.sub.s, w.sub.s) given in the
Table.
TABLE 1B h.sub.s.backslash.N.sub.s N.sub.s h.sub.s 1 2 3 4 5 100 nm
13.448 13.396 13.344 13.293 13.243 1 .mu.m 9.721 7.595 6.232 5.283
4.586 2 .mu.m 7.595 5.283 4.051 3.284 2.762 3 .mu.m 6.232 4.051
3.001 2.383 1.976 4 .mu.m 5.283 3.284 2.383 1.87 1.538 0.1 mm 0.339
0.171 0.115 0.086 0.069
Table 1B. Calculated effective sheet resistances
.OMEGA./.box-solid. for a system comprising N.sub.s strips, where
each strip possesses a width of 0.15 mm and a height, h.sub.s, as
indicated in the Table.
TABLE 1C w.sub.s.backslash.N.sub.s N.sub.s w.sub.s 1 2 3 4 5 0.01
mm 12.232 11.181 10.297 9.543 8.891 0.05 mm 8.891 6.628 5.283 4.392
3.758 0.1 mm 6.628 4.392 3.284 2.623 2.183 0.15 mm 5.283 3.284
2.383 1.87 1.538
Table 1C. Calculated effective sheet resistances
.OMEGA./.box-solid. for a system comprising N.sub.s strips, where
each strip possesses a height of 4 .mu.m and a width, w.sub.s, as
indicated in the Table.
The effect of size on the conductance of a 15 .OMEGA./.box-solid.
(TEC 15) substrate with internal busbars is shown in Tables 2A and
2B below.
Two different systems are considered: System A: IB's comprise
Pt-strips (.sigma.=0.96.times.10.sup.5
(.OMEGA..multidot.cm).sup.-1), each 0.15 mm wide and 41 .mu.m high;
and System B: IB's comprise strips of DuPont 7713 Frit with a sheet
resistance of R.sub.s =3 m.OMEGA./.box-solid. at 25 .mu.m
thickness. Each strip is 1.5 mm wide and 25 .mu.m high.
The number, N.sub.s, of IB's is such that there is a fixed spacing
of 1 cm between busbars. Edge busbars are not represented in the
calculations (so, e.g., for a L cm.times.L cm system, there are
(L-1) IB's). In all cases, the underlying conducting sheet
possesses a sheet resistance of 15 .OMEGA./.box-solid..
TABLE 2A Calculated effective sheet resistance for Systems A and B
R.sub.Sheet for R.sub.sheet for Substrate Area System "A" System
"B" 5 cm .times. 5 cm 1.90 .OMEGA./.box-solid. 0.0250
.OMEGA./.box-solid. 10 cm .times. 10 cm 1.71 .OMEGA./.box-solid.
0.0222 .OMEGA./.box-solid. 30 cm .times. 30 cm 1.60
.OMEGA./.box-solid. 0.0207 .OMEGA./.box-solid. 100 cm .times. 100
cm 1.57 .OMEGA./.box-solid. 0.0202 .OMEGA./.box-solid.
The effective sheet resistance is useful for comparing substrates
of comparable size. However, an effective resistance (R), defined
as the effective sheet resistance multiplied by the area of the
substrate (thus possessing units of .OMEGA..multidot.cm.sup.2
/.box-solid.), is more useful for comparing substrates of different
sizes. Table 2B comprises the data for the effective resistance
(R), for each sheet, as a function of substrate size.
TABLE 2B Calculated effective resistances for Systems A and B.
Effective Resistance Effective Resistance Substrate Area for System
"A" for System "B" 5 cm .times. 5 cm 47.4 .OMEGA. .multidot.
cm.sup.2 /.box-solid. 0.624 .OMEGA. .multidot. cm.sup.2
/.box-solid. 10 cm .times. 10 cm 171 .OMEGA. .multidot. cm.sup.2
/.box-solid. 2.22 .OMEGA. .multidot. cm.sup.2 /.box-solid. 30 cm
.times. 30 cm 1440 .OMEGA. .multidot. cm.sup.2 /.box-solid. 18.6
.OMEGA. .multidot. cm.sup.2 /.box-solid. 100 cm .times. 100 cm
15700 .OMEGA. .multidot. cm.sup.2 /.box-solid. 202 .OMEGA.
.multidot. cm.sup.2 /.box-solid.
It is desired that the width of the internal busbars should be
small so that the active area of the EC device can be maximized.
Further, such narrow widths also minimize optical interference to
viewing through EC devices to which such internal busbars are
incorporated. Thus, narrow widths are less obtrusive to vision.
As used herein, unless specified to the contrary, the descriptors
"narrow or wide" refer to a "width" dimension parallel to the
surface of the feature being described, while the descriptors "thin
or thick" refer to a "thickness" dimension orthogonal to the
surface of the feature being described.
A preferred geometry of the IB's include patterns which are greater
than about 1 .mu.m in thickness, and most preferably greater than
about 10 .mu.m in thickness. Although any convenient material can
be used and formed by any convenient technology, materials and
technologies that allow such thick IB's to be deposited are
preferred. Examples of materials which are easy to deposit in these
dimensions are typically conductive inks, pastes, and frits.
Examples of the methods are described below.
Generally, the overall conductivity of the substrate does not
depend appreciably on whether the conductive electrode coating is
over the grid, around the grid, under the grid, or in some such
combination. In the present invention, if the grid is deposited on
the surface of the transparent conductor, the grid should be
prevented from reacting or corroding in the device through the use
of a protective barrier or passivation coating. The construction
and materials of such a barrier coating depends upon the degree of
reactivity of the grid material at the potentials encountered
during device operation.
The internal busbars of the present invention may not be directly
connected to other busbars such as edge busbars or such signal
leads. The internal busbars of the present invention can be termed
"floating" busbars. The signals are generally conducted to the
internal busbars of the present invention by the conductive layer
that is in contact with them. By such contact, the conductive
layer's conductive is effectively lowered because the internal
busbars of the present invention have lower conductivity than the
conductive layer they are in contact with. The IB's of the present
invention can be optionally connected to other busbars described
above, to other IB's, or to electrical leads. However, as discussed
below, an IB of the present invention can nevertheless receive an
applied signal by the IB's being "bridged" to other voltage sources
through the conductivity of the conductive layer the IB is in
contact with. There are applications such as, for example, those
that call for specific signals being applied to specific internal
busbars where the internal busbars of the present invention can
optionally be directly connected to a signal source.
In addition to a variety of lateral geometries, the IB's can occupy
a variety of transverse locations in a device. For example, a
pattern may be deposited on top of the TC. In a device of the
form
(where EC refers to an electrochromic film), for example, one may
deposit a grid pattern on TC1, on TC2, or on both TC's. Naturally,
the height of a grid on TC1 should be significantly less than the
cell gap (i.e., the thickness of the electrolyte/redox species
medium), preferably much less. For a grid deposited on TC2, one
must ensure that the thickness, morphology, and chemistry of the
grid do not adversely affect the EC film. Regarding thickness, if
the thickness of the grid is much less than that of the EC film,
then the grid has little effect on the shape of the EC film. If the
thickness of the grid is on the order of or greater than that of
the EC film, then the EC film may often form a noticeable "relief"
of the grid pattern (or it may even form in separate areas defined
by the grid pattern).
The durability of devices with the IB grid of the present invention
generally should be similar to devices without the IB grid. Any
durability test should yield the same result with or without the
grid. That is, the addition of the internal busbars of the present
invention should not affect the reliability and durability of the
devices. Accordingly, results of any durability tests to qualify a
device for a particular application are likely transferable, or can
be anticipated to be the same if such tests are repeated with the
devices having internal busbars. Because durability is one of the
key issues involved in developing a commercially viable device,
this is an important parameter. To ensure durability of these
devices, it has been discovered that it is preferred to deposit a
passivation layer on top of the internal busbars, particularly if
the IB's are deposited on top of the transparent ECE's. Materials
for passivation are described below.
As shown in FIG. 21, the "effective height" of the grid may be
reduced by embedding the grid conductor partially in the TC and
substrate. Internal busbar conductors 2102 are embedded in
substrate 2101. The formation of internal busbar conductor 2102 may
be done by any convenient way such as, for example, by etching or
ablating away a desired pattern in the substrate and then
depositing the desired grid material. The effective height of the
grid may be reduced by embedding it partially in the glass as well
as the TC. One can etch or ablate away consecutively the TC coating
and the substrate, followed by depositing the desired grid
material. Alternatively, one can deposit the grid onto, or embed
the grid into, the glass before the TC is deposited. The portion of
busbar conductors 2102 that are above the surface plane of
substrate 2101 is removed until the surface and the busbar
conductors are at substantially the same plane 2103.
In one embodiment, the grid is partially embedded into the glass
and then the surface is planarized by, for example, polishing to
produce a structure as shown in the process in FIG. 21. Planarizing
may also be done by depositing additional material on to the
substrate so that the top surface of this added material is
coplanar with the grid. Although FIG. 21 shows conductors 2102
having circular cross section such as commonly found in a wire, it
could be of another convenient shape, such as rectangular.
Additionally material can be deposited, for example, from
solutions, or by physical vapor deposition, etc. Some examples of
such materials are polyimide, sol-gel deposited oxides and
organic/inorganic hybrids.
A TC is then deposited on the resulting planarized surface and the
resulting glass.vertline.TC substrates used in the same manner as
they are typically used. This process of the present invention has
the distinct advantage that the more chemically active components
of the device such as the EC film and the electrolyte are not
directly exposed to the IB grid material.
Except for the glass substrates, the layers in single substrate
devices (See, for example, FIG. 1E) are generally each quite thin
(typically in the 100's of nm). It is therefore particularly
preferred to use IB's which are fully embedded under the TC in such
devices. The IB on the outer TC (layer 103' of FIG. 1E) could
consequentially be of any thickness since it will protrude on the
outside of the device.
Whether it is desirable to include IB's on one or both TC's in a
device depends on a variety of factors, including the required
response time and coloration uniformity characteristics and the
cost of manufacturing the devices. Devices generally display faster
response times and greater coloration uniformity with the IB's
implemented on both TC's.
IB Dimensions
The dimensions of the IB's width and depth can be varied throughout
a substrate. As shown in FIG. 22, EC device 2210 has conductive
transparent substrate 2201 transversed by narrower internal busbars
2202 and wider internal busbars 2203. Narrower internal busbars
2202 and wider internal busbars 2203 are separated by gaps 2208
from edge busbar 2204. Gaps 2208 are bridged by conductive
transparent substrate 2201. Narrower internal busbars 2202 and
wider internal busbars 2203 optionally connect directly to edge
busbar 2204.
By combining, for example, narrow and wide IB's one can enhance the
conductivity of the substrate while maximizing its transmission.
However, while incorporating the use of wider IB's decreases their
resistance (and thus advantageously decreases the effective
resistance of the TC), it also affects the apparent transmission of
the device. The transverse or primarily transverse direction is
usually the direction of most importance for the optical properties
of the devices. Accordingly, increasing the depth (or height) of
the IB's is advantageous when compared to increasing the width of
the IB because increasing the depth will typically have a much
smaller adverse effect on the cosmetic appearance and/or the
apparent transmission of the devices than increasing the width.
Another component of the present invention is the use of IB's which
will be optically less prominent, by making the IB's much deeper
than they are wide. For example, defining the aspect ratio,
r.sub.ib, as the effective width of the internal busbar structure
divided by its effective height (thickness), it is generally
desirable to have rib smaller than 1, for optical transmission
applications where a viewing path is through the surface on which
is deposited the busbar structure.
The reason is that, if one is viewing parallel to the height
(thickness) of the IB, then increasing the thickness while the
other dimensions of the IB remain constant does not substantially
affect the appearance of the device; but such increased thickness
does desirably reduce the resistance of the IB (and therefore
desirably reduces the effective resistance of the corresponding
TC). It is therefore generally desirable that the height direction
of the IB's be parallel to the primary viewing direction for such
applications.
Most commonly, this means that the height direction of the IB's
should be transverse to the plane of the substrates of the device.
But for some devices such as, for example, an automotive
windshield, the primary viewing direction might be at some angle to
the approximate plane of the windshield. In such applications it
would be preferable to implement the IB's such that their height
direction is parallel to such slanted viewing direction. As shown
in FIG. 23, device 2301 has internal busbars 2302 embedded in
substrate 2303 at an angle parallel to the viewing direction
2305.
Another consideration is the need to provide a contiguous channel
within the device that allows the electrolyte fluid to flow
throughout the gap during filling in order to minimize
manufacturing difficulties. Referring to FIG. 31A, a device 3101
has internal busbars 3102 disposed such that no internal busbar
blocks a contiguous channel. Internal busbars 3102 are in contact
with only one device edge and extend only to the other device edge,
thereby forming a contiguous channel 3103. If the device is filled
with the electrolyte after edge sealing (such as by vacuum
back-filling), only one fill hole is required to perform the
filling task.
Similarly, FIG. 31B shows a device 3110 where internal busbars can
extend from one device edge to the other device edge. The internal
busbars are arranged in a staggered configuration. Consequently,
although internal busbars 3102' might extend from one device edge
to the other device edge, and each internal busbar 3102' might be
thicker than one half the gap distance, their staggered arrangement
forms a contiguous channel 3103' which allows easy filling of
device 3110, with electrolyte fluid, without interruption.
FIG. 31C shows a device 3120 which has internal busbars 3102" that
can extend from one device edge to the other device edge, and that
can be in an overlapping relation. Internal busbars 3102" are,
however, in alternate ramped geometries which form a contiguous
channel 3102" which allows easy filling of device 3120, with
electrolyte fluid, without interruption.
FIGS. 31B and 31C show embodiments of the present invention in
which the sum of the thicknesses of the internal busbars is larger
than the cell gap distance. Yet, the innovative geometries of the
present invention allows such internal busbars use without any
problems of electrical shorting or interrupted electrolyte fluid
continuity. As described above, the width of the internal busbars
should be small so that the active area of the overall EC device
can be maximized. The resistance of internal busbars with narrow
width can be nonetheless low because the height (thickness) of the
internal busbars can be made effectively thick. As described above,
geometries and patterns that form IB's having thicknesses greater
than about 1 .mu.m are preferred, and most preferred are
thicknesses greater than about 10 .mu.m. FIGS. 31B and 31C show how
such thicker dimensions can be used without causing the gap
distance to be disadvantageously thick.
Auxiliary Uses for IB's
The IB's included in devices under the present invention may be
used for additional purposes, and these may or may not require
modification of the IB design. For example, the IB's may be used as
Joule heating elements for purposes such as de-fogging. For this
purpose, it is desirable to pass current through the IB's
independently of current being used to color or bleach the
device.
One means for implementing this purpose according to the present
invention includes providing for separate addressing of the two
ends of a set of IB strips. FIG. 24 shows a device 2410 with an EC
assembly 2401 having two internal busbars 2402 over the layers of
TC 2403. Applying a voltage V1 and V2 of equal values across the
two ends will induce a current flow along each of the internal
busbars 2402 but will not result in EC activity in device 2410
because, with equal voltage potentials at each end, there is no
current path or potential drop transverse to the device. If it is
desired that EC activity and heating occur contemporaneously, the
signals can be adjusted accordingly to provide for a current path
and a potential drop transverse to the device by changing V1 and V2
to be unequal. For most EC devices the voltage difference needed
between V1 and V2 is less than 2 volts.
If IB's are implemented on both TC's of a window-type device,
separate heating of both TC's without inducing EC activity requires
balancing of the lateral voltage potentials so that there is no
transverse potential. If simultaneous coloring is desired, the
potentials can be adjusted accordingly.
The IB's may also be used as antennae for electromagnetic signals.
For example, one can use a strip IB as a monopole antenna, letting
one end float electrically and connecting the other end to the
appropriate signal processing electronics such as, for example, a
radio receiver. To obtain a larger signal, the signals from a set
of strip IB's forming well known antennae geometries may be
combined and the combined signal appropriately processed. Other
patterns of IB's forming well known antennae geometries may be used
to optimize the antenna functionality. If desired, IB's may also be
used as transmitters following well known transmitter grid
geometries.
IB's may also be used to provide or enhance the effective shielding
from unwanted electromagnetic waves or interference. The
penetration depth (or "skin depth") of electromagnetic waves into
the devices may be decreased by increasing the effective
conductivity of the TC layers. In addition, specific IB patterns
may be employed such as, for example, forming a part of a Faraday
cage to provide optimal shielding for a particular class of
electromagnetic waves.
Separately-Addressable IB's
In an embodiment of the present invention, IB's form a single
addressable array. FIG. 25A shows a device 2501 with internal
busbars 2505 arranged at an angle to and proximate to a busbar 2507
with proximate gaps 2508 between busbar 2507 and each internal
busbar 2505. Proximate gaps 2508 are bridged by conductive layer
2509 on substrate 2510. Busbar 2507 can be an internal busbar or an
edge busbar. Busbar 2507 and internal busbars 2505 form a single
addressable array 2503 powered by a conductor 2504. Optionally,
each internal busbar 2505 is directly connected to busbar 2507.
In another embodiment of the present invention, the IB's are made
to be separately addressable. FIG. 25B shows a device 2502 with
separately addressable internal busbars 2506, each separately
powered by separate conductors 2504.
One can use the separately addressable IB's to obtain an added
measure of control over the spatial distribution of the coloring
and/or bleaching of an EC device. Whether one needs to be able to
address separately the IB's on one of the TC's or on both of the
TC's depends upon the degree of control required.
One can utilize the separately addressable busbars (or separately
addressable busbar groups) to have an EC device (e.g., a sunroof or
windshield) that has differential coloration from one side to the
other, or from top to bottom, etc. Such individual control can
produce a number of effects such as, for example, a gradient
effect, a shade effect, or a geometric pattern effect.
One can employ light sensors and use the signals from the sensors
to determine the appropriate signals to apply to the separately
addressable IB's to obtain the desired spatial distribution of
coloring or bleaching. For example, for an automotive sunroof, one
can use light sensors to effectively track the position and
intensity of the sun and then color more deeply the appropriate
regions of the sunroof. In addition, information (obtained either
automatically or manually) regarding the presence and positions of
occupants of the automobile may be combined with the signals from
the light sensors to determine the appropriate signals to apply to
the separately addressable IB's to obtain an appropriate coloring
or bleaching pattern. The light sensors should be situated such
that they provide effective indications of the light intensity from
a variety of directions. The presence and positions of occupants of
the automobile may, for example, be sensed via transducers in the
seats and/or by detecting the status of the seatbelts.
Under the present invention, a variety of "Smart Devices" can be
made by using the signals derived from a system of sensors to
determine the appropriate drive signals to be applied to the
individually-addressable IB's and edge busbars in EC devices.
Conductive frits are usually pastes and liquids (also termed inks)
of a conductive material in a carrier. The carrier typically cures
or typically is eliminated during a post-application process such
as subjecting to elevated temperatures. Conductive frits for IB can
be deposited by any convenient method such as, for example, X-Y
Motor Painting/Screening, Doctor Blading/Silk Screening/Circuit
Printing, Chemical Vapor Deposition and Physical Vapor Deposition
(CVD and PVD):
1. X-Y Motor Painting/Screening: For certain conductive materials,
which are applied in the form of viscous liquids, a programmable
X-Y table with a fluid dispenser may be utilized to apply the
desired pattern to the substrate. The thickness and width of the
conductive line is determined by factors such as the size of the
dispenser tip opening, the viscosity of the fluid, the dispenser
line pressure and the lateral speed of the dispensing tip relative
to the substrate, and the distance between the dispensing tip and
the substrate. Low viscosity molten metals may also be used for the
busbars. These could be sprayed or processed by soldering or
welding. These methods could be assisted by ultrasound or other
energy imparting means to promote uniformity and/or better adhesion
to the substrate.
2. Doctor Blading/Silk Screening/Circuit Printing: This method
involves the forcing of a viscous liquid through narrow openings in
an appropriate mask, to be deposited on a substrate in a pattern
determined by the mask design. This mask may consist of any type of
tape, film, or other mask material, such as a silk-screen-like
item, placed on top of the substrate, with channels or isolated
voids in a desired pattern. An excess of the fluid is then placed
at one end of the mask, then a uniform, flat tool (such as a
"squeegee" or similar implement) is dragged across the mask,
forcing the fluid through the pattern troughs onto the
substrate.
Another alternative is to silkscreen, or otherwise use a doctor
blade to deposit uniform layers of photoprintable thick film
compositions. The internal busbar pattern is then formed by
exposing the deposited film to certain wavelengths of light through
masks and followed by chemical processing. The passivation
materials for internal busbars such as certain dielectric materials
can be similarly processed. The advantage of this over conventional
silkscreening is to get finer resolution and/or higher densities of
conductive lines.
3. Chemical Vapor Deposition and Physical Vapor Deposition (CVD and
PVD): CVD is a known process which deposits a coating by
decomposing a chemical vapor to provide the depositing material.
PVD is a known process which deposits a coating by vaporizing a
material and then redepositing this in a substrate in a vacuum
chamber. CVD and PVD may be assisted by energy imparting sources
such as plasma, ionized beams, microwave, etc.
In these methods, patterns are applied by placing either a shadow
mask over the substrate and coating directly onto the surface, or
by using photolithographic technology to apply a photoresist mask
to the substrate, coating that assembly with metal, and then
stripping the photoresist layer away, leaving the metal
pattern.
Some exemplary frit, inks and conductive adhesives that may be
employed in this invention include:
Frits:
DuPont Electronic Materials, Wilmington, Del., Silver-Bearing
Conductors: DuPont Silver Thick Film Composition, Nos. 1991, 1992,
1993, 1997; DuPont Silver Thick Film Composition, #7713; and DuPont
Solamet Photovoltaic Compositions such as #E64885-52A.
DuPont Gold-Bearing Conductors.
DuPont Fodel Photoprintable Conductors DC201 and DC010.
Ferro Silver Paste FX 33-246 available from Ferro Inc., Santa
Barbra, Calif.
Metal Inks:
Engelhard Electronic Materials, East Newark, New Jersey,
Metallo-Organic Inks: Platinum Inks such as #05X, Gold Inks such as
#A3622, and Silver Inks such as #R2/321 and low temperature cured
flexible materials such as #M5860.
Conductive Epoxies, Silicones, etc.:
Grace Specialty Polymers, Emerson & Cuming Inc. (Woburn,
Mass.), Minico M 4200 Flexible Silver Buss Bar; 4xxx series
materials; Eccocoat CT 5030 A/B Flexible/Rigid Buss Bar; Minico M
6xxx series silver/copper materials.
When devices are fabricated that use two substrates, such as those
described in U.S. Pat. Nos. 5,142,407, 5,241,411 and 4,761,061, one
or both of the substrates may have added internal busbars according
to the present invention.
FIGS. 26A and 26B show two configurations of various grid patterns
according to the present invention that do not extend to the edges.
FIG. 26A shows a device 2608 having a perimeter busbar 2602 on
substrate 2601. Substrate 2601 has a conductive layer 2615 on its
surface. A series of internal busbars 2603 form a crosshatch
pattern. Internal busbars 2603 can be on, in, and/or below
conductive layer 2615. The perimeters of each internal busbar 2603
are in contact with conductive layer 2615.
FIG. 26B shows a device 2609 having a series of internal busbars
2604 forming a parallel pattern. Neither series of internal busbars
2603 or 2604 touch perimeter busbar 2602. As a result, when an EC
device is fabricated using two substrates, the grid pattern an be
completely enclosed in the device. The internal busbars conduct a
current that travels from the perimeter conductor through the
conductive layer 2615 to the internal busbar. This may be
advantageous, since the adhesive used to seal the edges of the two
substrates need not be modified in composition and no change in
processing parameters is needed for ensuring good adhesion to the
internal busbars and for accommodating the change in substrate
topography.
FIG. 26C shows a device 2610 having a coiling internal busbar 2605
which is in contact with conductive layer 2615 at the entire
perimeter of internal busbar 2605. Coiling internal busbar 2605 has
higher conductivity than conductive layer 2615, which serves to
lower the overall resistance of conductive layer 2615, thereby
making more homogeneous the applied signal to conductive layer
2615. Coiling internal busbar 2605 can stand alone as shown.
Coiling internal busbar 2605 also can be formed in close proximity
at its outer coil to a perimeter busbar (not shown). Alternatively,
the coiling internal busbar can be attached directly to a signal
power by leaving a portion of the coiling internal busbar exposed
and attaching a signal wire to the exposed portion.
Since the current at the perimeter has to flow only through gaps of
a short distance through the transparent conductors to the internal
busbars of FIGS. 26A, 26B, and 26C, the resistance drop will be
negligibly small across such gaps. This use of the transparent
conductor to connect an internal busbar to the primary busbar has
not been discussed or disclosed in any prior art described
above.
A passivation layer may be deposited using similar techniques
described previously. If certain materials and methods are used to
deposit the grid pattern such as silk-screening of metal frits,
then post-treatment such as curing or hardening with time, heat,
radiation (UV, visible, IR, microwave) may be required. The
passivation layer is typically deposited after the above
post-treatment. Similar types of post-treatment procedures may be
required to harden the passivation layer.
The post-treatment for the grid pattern may also result in an
in-situ formation of a passivation layer on the surface. The
in-situ formed surface may consist of a phase separated inert
material, an oxidize portion, a nitride portion, etc. This will
also depend on the atmosphere and temperature conditions under
which such post-treatment is carried out. This passivation layer
may be sufficiently passivating to be incorporated in these
devices. Treatment where a part of the exposed grid pattern becomes
passivated could also be done when the grid patterns are deposited
by physical and chemical vapor deposition. The surface of these may
be passivated using oxidation, nitriding, heat, laser, plasma, or
ion bombardment assisted treatments. The passivation layer may
consist of organics, inorganics or hybrid materials. Adhesives such
as, for example, non-conducting epoxy adhesives, urethanes,
acrylates, or polyesters could be deposited for passivation. These
may be the same materials that are used for making device seals.
The materials may be cured by heat and/or radiation, such as UV, IR
or microwave. The viscosity and the application procedure can be
adjusted so that the desired thickness is obtained.
The materials can be applied by any convenient method such as, for
example, being screened, dispensed, sprayed, or painted. Sol-gel
methods could also be used to deposit oxides and polyceramics as
passivation layers. Examples of such materials are alcoholic or
non-alcoholic based solutions of metal alkoxides, nitrides,
halides, or mixtures thereof, or solutions of reactive metallic
precursors with organic complexing agents. Further, these oxides
may be inert such as silica or could be conducting such as indium
tin oxide and doped tin oxide. Preferably the passivating materials
should be non-conductive, both ionically and electronically.
Electronically conducting materials which may be used as
passivating materials are those which are used in making
transparent ECE's such as doped tin oxide and indium tin oxide.
They should not also be attacked, swelled, or interact with the
layers that come in contact with such as electrochromic layers, ion
storage layers, electrolytes, etc. Examples of some commercial
encapsulants/passivation layers that could be silk-screened include
#A3840, #A3560, and #A3563, made by Engelhard. An example of a
photoprintable passivation layer is Fodel DG211 from DuPont
Electronic Materials.
Electrochromic devices use several transparent conduct or s that
are not reactive while the other components such as electrochromic
layers, counterelectrodes, and redox materials in the electrolyte
necessarily participate in the electrochemical activity required
for electrochromic operation. Thus, non-reactive materials are
defined as those that lie outside the electrochemical potential
range that is utilized for operating the EC device. Also materials
that are insulators and/or do not transmit or get intercalated with
ions under the above operating conditions and will not change their
physical properties in the cell (such as dissolution in the liquid
electrolyte if used) can also be considered as non-active.
Materials such as many polymers such as epoxies, polyimides,
acrylics, urethanes, and inorganics such as dense silica, alumina,
several other oxides, silicates, and organo-silicates can be also
considered non-reactive. For some devices, metals such as gold and
platinum may also be considered non-reactive. Thus these metals may
be used for busbars without additional passivation layers. There
may even be thick layers of transparent conductors such as ITO, in
a thickness that is conductive enough for the busbar, but not
transmissive enough to be called TC (transparent conductor).
For designs where the internal busbars extend to the perimeter edge
of the substrate, the passivation layer may extend to the edge of
the substrate, or stop short of the edge so as to only be in the
interior of the device. In the latter case, the internal busbars
can be electrically contacted with the edge busbars (for example by
using wires, tapes, conductive adhesives, solders, or wire clips).
The novel edge busbars of the present invention may also be used in
conjunction with the novel internal busbars of the present
invention.
The conductivity of the substrate can also be enhanced through the
use of a wire pattern embedded in a substrate (the substrate may be
constructed from glass, plastic, or some other material). This wire
pattern substitutes for the grid pattern described above. If the
substrate is essentially electrically insulating, and if the
conductive pattern is entirely embedded in the insulating
substrate, then it is generally necessary to connect electrically
the conductive pattern and the transparent conductor. This may be
done, for example, by drilling holes though the substrate up to the
metal grid and then filling the holes with a conductive material.
FIGS. 27A, 27B, 28, and 29 illustrate this concept, including
different methods of ensuring transparent conductor/plug
contact.
FIGS. 27A and 27B show a device 2710 with a substrate 2705 covered
with a transparent conductor layer 2704. Internal busbar conductors
2702 are embedded in substrate 2705. Conductive plugs 2703 lead
from the. surface of device 2710 to electrically contact internal
busbar conductors 2702. In this example, transparent conductor
layer 2704 was applied after the holes for plugs 2703 were made but
before plugs 2703 were formed.
FIG. 28 shows a device 2801 formed by attaching internal busbars
2802 to a surface 2807 of a substrate 2803. Holes 2805 are formed
effective to extend from an opposite surface 2808 of substrate 2803
to internal busbars 2802. Conductive plugs 2804 are formed
effective to extend from internal busbars 2802 to opposite surface
2808. Transparent conductive layer 2806 is then formed on opposite
surface 2808, contacting conductive plugs 2804, thereby being in
electrical contact with internal busbars 2802.
FIG. 29 shows a device 2901 where direct addressing of the internal
busbar conductor was not necessary. Device 2901 has an internal
busbar conductor 2902 embedded in substrate 2904. A conductive
layer 2903 provides electrical contact between transparent layer
2905 and internal busbar conductor 2902. Inert filler plug 2906
fills the hole. Transparent conductor 2905 is applied after the
hole that provide access to internal busbar conductor 2902 is made.
Then conductive layer 2903 is formed in the hole. Finally, inert
filler plug 2906 is formed.
If the conductive pattern is not entirely embedded in the substrate
(i.e., if it contacts the transparent conductor) or if the
substrate is sufficiently conductive, a separate conductor is
generally not necessary.
Internal busbars can also be used to make devices with those
substrates on which only low conductivity transparent ECE's can be
deposited. Typically, transparent ECE's such as indium tin oxide
and doped tin oxide are deposited at high temperatures (in excess
of 200.degree. C.) to get good conductivity. Most of those
materials, when deposited on plastics, at lower temperatures, are
less conductive. Thus, the use of EB's as described above in
conjunction with lower conductivity transparent ECE's would result
in high conductivity substrates which will be attractive for
electrochromic devices.
The Examples which follow are intended as an illustration of
certain preferred embodiments of the invention, and no limitation
of the invention is implied.
Example 3
Strips of silver frit paste (DuPont # 7713) were deposited by
silk-screening onto a 3 inch.times.3 inch (7.5 cm.times.7.5 cm) TEC
15 substrate. The substrate was then heated under ambient
atmosphere according to the following four step procedure; Step 1:
Temperature raised from 25.degree. C. to 100.degree. C. at
10.degree. C./min and held at 100.degree. C. for 15 minutes. Step
2: Temperature raised from 100.degree. C. to 325.degree. C. at
10.degree. C./min and held at 325.degree. C. for 10 minutes. Step
3: Temperature raised from 325.degree. C. to 600.degree. C. at
10.degree. C./min and held at 600.degree. C. for 10 minutes. Step
4: Temperature lowered from 600.degree. C. to 25.degree. C. at
10.degree. C./min.
After firing the width and depth of the silver lines were measured
using surface profilometry and found to be 0.2" (5.1 mm) wide and
15 .mu.m deep. The spacing between the lines was 1.0" (25.4
mm).
Examples 4, 5, 6, 7, and Comparative Example 3
The "TEC-Glass" products, commercially available from
Libby-owens-Ford Co. (Toledo, Ohio), are manufactured by an on-line
chemical vapor deposition process. This process pyrolytically
deposits onto clear float glass a multi-layer thin film structure,
which includes a microscopically thin coating of fluorine-doped tin
oxide (having a fine grain uniform structure) with additional
undercoating thin film layers disposed between the fluorine-doped
tin oxide layer and the underlying glass substrate. This structure
inhibits reflected color and increases light transmittance. The
resulting "TEC-Glass" product is a non-iridescent glass structure
having a haze within the range of from about 0.1% to about 5%; a
sheet resistance within the range of from about 7 to about 1000
ohms per square or greater; a daylight transmission within the
range of from about 77% to about 87%; a solar transmission within
the range of from about 64% to about 80%; and an infrared
reflectance at a wavelength of about 10 .mu.m within the range of
from about 30% to about 87%.
A TEC 15 substrate (3 inch.times.3 inch; 7.5 cm.times.7.5 cm) was
silk-screened with silver paste as described in Example 1, where
the length of the silver strip was incrementally varied in such a
manner as to leave an equal distance between edges, at right angles
to the strips, of the glass substrate as shown in FIG. 26B. The
distances of the silver strip from the edge for Examples 4, 5, 6,
and 7 are 0.0 mm, 1.0 mm, 3.0 mm, and 7.0 mm respectively. The
resistance of the substrate was measured by soldering a metal strip
2 mm wide at both edges of the substrate which were at right angles
to the internal silver strips to serve as a representative portion
of a perimeter busbar. By applying a voltage across the soldered
strips the resistance was measured for different increments of
distance of the silver strip from the perimeter busbar. The results
are listed in the following Table 3.
TABLE 3 Distance of Silver Strip Resistance to From Edge Substrate
Example (mm) (.OMEGA.) 4 0.0 0.1 5 1.0 1.2 6 3.0 1.9 7 7.0 3.2
The Comparative Example 3C, a TEC 15 substrate with no internal
silver busbars had a resistance of 15 .OMEGA.. By comparison, as
shown in the table, Example 4, the substrate with internal silver
strips extended fully to the perimeter busbars had a resistance of
0.1 .OMEGA.. Even in Example 7, with the silver busbars as far as 7
mm from the perimeter busbar, the resistance is decreased to 3.2
.OMEGA. from the Comparative Example's 15 .OMEGA..
Example 8
Internal silver busbars were prepared as described in example 3,
except that after the four step firing procedure the metal strips
were over-coated with an epoxy based polymer for passivation and
cured at 120.degree. C. for one hour.
Comparative Example 4C
A 3".times.3" (7.5 cm.times.7.5 cm) TEC 15 substrate coated with
380 nanometers of WO.sub.3 according to the method set forth in
U.S. Pat. Nos. 5,252,354, 5,457,218 and 5,277,986 and a counter
electrode of TEC 15 of similar size was made into a cell using an
epoxy seal containing 210 .mu.m spacers. The two electrodes were
positioned so that they were slightly off-center exposing a region
at either end for application of a metallic busbar. Prior to
assembly the counter electrode had two holes drilled in it for
application of the electrolyte. The cell was filled with
electrolyte containing 0.01M LiClO.sub.4 and 0.05M ferrocene in a
60:40 volume % mixture of propylene carbonate and tetramethylene
sulfone and the fill holes plugged with epoxy. The conductive
surfaces which protruded from either side of the cell were
ultrasonically soldered with lead-tin-cadmium-based solder. Wires
were then attached to these contacts. The electrochromic
performance of the device was determined by placing the cell in a
spectrometer and following the color kinetics at 550 nm while
applying a coloring potential of 1.3 volts followed by a bleaching
potential of -0.3 volts. In the transmissive (bleached) state the
cell had a transmission of 77% and in the fully colored state a
transmission of 10% T. At a coloring potential of 1.3 volts the
cell took 46 seconds to color from 70% T to 10% T and 47 seconds to
bleach back to 70% T.
Examples 9, 10, 11 and Comparative Example 4C
Four electrochromic cells were prepared as described in comparative
Example 4C where the composition of the electrodes were varied as
follows; Cell A, Comparative Example 4C, had conductive electrodes
with no internal busbars. Cell B, Example 9, had internal busbars
on the working electrode (WO.sub.3) only. Cell C, Example 10, had
internal busbars on the counter electrode only. Cell D, Example 11,
had internal busbars on the both electrodes.
In all cases, Examples 9, 10, and 11, the internal busbars were
deposited as described in Example 8. The cells were colored at 1.3
volts for 90 seconds and bleached at -0.3 volts for 90 seconds. The
color kinetic data for the cells is shown in the following Table
4:
TABLE 4 Time to color from Time to bleach from 70% T to 10% T 10% T
to 70% T Cell Seconds Seconds Cell A 89 89 Cell B 74 65 Cell C 89
89 Cell D 56 58
Comparative Example 5C
An electrochromic cell was prepared as described in Example 8 with
conductive electrodes which contained internal busbars without a
passivation layer. The cell was cycled at 70.degree. C. at a color
potential of 1.3 volts for 15 seconds, long enough to colorize,
followed by being bleached for 45 seconds at -0.3 volts. After
5,000 such cycles the cell showed visible reaction of the silver
strips within the cell. This resulted in a degradation in the
cell's optical properties.
Example 12
An electrochromic cell was prepared as described in Example 8,
containing internal silver busbars, on both electrodes, with a
protective epoxy overcoat. At a coloring potential of 1.3 volts the
cell colored from 70% T to 10% T in 8 seconds. The cell was cycled
at 70.degree. C. under a coloring potential of 1.3 volts for 15
seconds and a bleach potential of -0.3 volts for 45 seconds. After
5,000 cycles the cell showed no visible reaction of the internal
busbars in the cell nor degradation of the cell's electrochromic
performance.
Example 13
Silver strips were deposited onto TEC 15 as described in example 3,
and overcoated with a layer of indium tin oxide (ITO). The ITO was
deposited by electron beam (E-beam) evaporation and deposited
directly on top of the TEC 15 and the silver strip lines through
the use of a mask. The E-beam target was an indium tin oxide
composite and the thickness of the ITO layer thus formed was 500
nm. Two of these TEC 15 substrates having the described electrodes
were used to make an electrochromic cell as described in example 9.
Under a coloring potential of 1.3 volts the transmission at 550 nm
changed from 76% T to 8% T. It took 14 seconds to modulate from 70%
T to 10% T at 1.3 volts, while it took 23 seconds to bleach back to
70% T at -0.3 volts.
Example 13B
Silver strips were deposited onto TEC 15 as described in example 3,
and overcoated with a layer of Sol-Gel derived antimony doped tin
oxide (ADT). The ADT precursor was prepared as described in U.S.
Pat. Nos. 5,525,624 and 5,457,218. The electrodes were made into an
electrochromic cell as described in example 9. At a coloring
potential of 1.3 volts the cell colored from 70% T to 10% T in 19
seconds. At a potential of -0.3 volts it bleached back to 70% T in
20 seconds.
Example 14
Fodel materials and processes (from DuPont) and the like can be
used to deposit busbars which are less than 100 .mu.m in width.
These lines are practically invisible to the eye, depending on the
distance between the eye and the substrate on which the lines are
deposited. For example, a normal eye subtends a small enough angle
with lines of widths of 100 .mu.m from a distance of 19 inches that
the line is not discernible (about 0.01 degrees). Thus, any angle
equal to or smaller than 0.01 degrees can be considered as
invisible. Such busbar widths that form these angles, depending
upon the distance of the substrate from the observer, can be
utilized with little or no interference with vision. For example,
50 .mu.m wide lines (6 .mu.m thick) spaced at a distance of 0.75 cm
are expected to give the same overall conductivity to the
substrates as lines which are 100 .mu.m wide (6 .mu.m thick) and
spaced 1.5 cm. Both of these widths and line spacings are expected
to give photopic transmissions in excess of 70% when deposited on
conductive glass (such as TEC glass from LOF) with a resistance of
8 or more ohms/square.
Although the above description is for chromogenic windows, these
principles can also be utilized to develop non-chromogenic windows
which can be defrosted by applying an electrical voltage at the
edges but without any visible obstruction from conductors in the
center of the window. These windows can be used in various
applications where frost-free characteristics are desired. Examples
of such application are in aircraft and automotive windows and
mirrors. For an automotive windshield, these can be deposited on
glass before lamination. After lamination, preferably these lines
reside inside of the laminated area so that they are not scratched.
They can also be used for other windows and mirrors which are not
laminated, and to further enhance their scratch resistance they may
be coated with hard transparent materials (for example, see U.S.
patent application Ser. No. 09/099,035, filed Jun. 18, 1998, which
is incorporated herein by reference). Since high temperatures
(typically 500 to 800.degree. C.) are required to fire these lines,
this could be accomplished simultaneously while the glass is being
bent and/or strengthened (or tempered) which may be necessary for
these products. As described above, based on the angular
calculations, widths of these lines can be wider for rear
automotive windows as compared to the windshields, since the latter
are closer to the observer. Further, the material in these widths
can also be used to deposit antennas on glass (such as automotive
windows) which are invisible, i.e., the window appears transparent
although a patterned antenna is printed using these conductors and
processes.
Example 15 and Comparative Example 6C
Two 6".times.3" (15 cm.times.7.5 cm) sized electrochromic cells
were prepared. TEC 15 was used as the transparent conductor in each
cell. Example 15 had an internal busbar while Comparative Example
6C did not. The cell without the busbar, Comparative Example 6C,
was assembled similarly to the assembly described in Comparative
Example 4C. The spacing between the substrates, however, was 88
micrometers. The two electrodes were positioned with an offset so
that about 0.25 inch (0.63 cm) of each electrode strip, at either
of the 3" (7.5 cm) ends of the substrates, was exposed. To these
exposed edges, a solder was applied by a heated ultrasonic
soldering system (Sunbonder from Sanwa Components USA, San Diego,
Calif.). The solder used was Cerasolzer 186 (obtained from Sanwa
Components US), and had an average thickness of about 20
micrometers.
The second cell, Example 15, also had a gap 88 micrometers thick
and was made with both internal busbars and edge busbars as taught
in this invention. In Example 15, edge busbars and an internal
silver frit busbar were applied to three contiguous edges, via an
x-y dispensing technique, similar to that shown in FIG. 33A.
The frit layers were fired with the four-step procedure as in
Example 3 and then passivated as in Example 8 using a black colored
bisphenol A based epoxy adhesive. This frit/passivation pattern was
applied to both the substrates. The width of the frit line was
about 0.7 mm and thickness of the frit line was between 10 and 15
micrometers. The thickness of the passivation layer was about 30 to
40 micrometers with a width of about 1.5 mm so as to completely
cover the frit to form an encapsulation around the frit. One of the
substrates was then coated with tungsten oxide, assembled, and
filled as described in the Comparative Example 4C. The frit pattern
was identical on both the substrates except that the frit line
pattern was lightly offset so that the frit lines on the two
substrates were next to each other rather than opposed or on top of
each other. This was done to ensure that any local bumps would not
lead to any electrical shorting and that the cell gap is maintained
at 88 micrometers.
Similar to that geometry shown in FIG. 33B, the internal busbar was
formed by one of the frit lines, while the other three frits formed
an edge busbar since they were outside the cell seal area. Further,
the soldered busbar which was applied in addition to the frit
busbar on the edge, reinforced the conductivity on that edge, while
providing a means to attach a soldered electrical lead. The silver
frit and the soldered busbar were touching each other in this
Example.
Example 15 and Comparative Example 6C were colored at 1.3 volts for
60 seconds and bleached at -0.3 volts for 60 seconds. The plots of
transmission versus time are shown in FIG. 34A, and the concomitant
current flow through the devices is shown in FIG. 34B. In FIG. 33B,
DuPont Frit type 7713 was used to form the frit layers.
It can be seen that in Comparative Example 6C, the cell without the
internal busbar, the coloring reaction is slow and the depth of
color is small. By contrast, in the cell with the internal busbar,
Example 15, the coloring and bleaching reactions are faster and the
depth of coloration is much higher because the internal busbars are
able to supply much higher levels of current when needed during
coloration and bleaching. Thus, devices that demand high currents
any time during coloration or bleaching will particularly benefit
from this invention. Typically, EC devices requiring currents in
excess of 0.1 mA during coloration or bleaching will benefit
most.
Intermittent Potential Circuitry
As described previously, the coloring voltage only needs to be
applied intermittently, depending on the length of the color state
memory, after sufficient coloration has been achieved. For example,
if the memory of the device was longer than the color duration
required for the particular application to be colored, then the
coloring potential effectively could be applied just once and then
turned off (i.e., the device is left in non-powered open circuit
mode). The potential can then be applied again when the device's
light transmission needs to change, e.g., while bleaching or
changing its transmission to a different desired level. However,
under certain circumstances, it might be necessary to keep the
device in a desired state of transmission for periods that are
longer than their color state memory.
In the present invention, consider for example the case where a
coloring potential is initially applied which is removed after the
device attains the desired color, i.e., the device is kept in an
open circuit. The device is thus allowed to gradually bleach with
time, for a period t.sub.1, as a result of its limited color state
memory. Before the device completely bleaches, the coloration
potential is reapplied for a duration of time t.sub.2. This process
can be continued indefinitely for as long as the device needs to be
kept in the particular colored state before a different voltage is
required to be applied to change the device's light transmission
(e.g. bleach potential).
The period t.sub.1, after which the coloration voltage is
re-applied, depends in part on the extent of color change that is
allowed before it might become obvious to the user that the device
light transmission is changing. This allowable change in photopic
transmission, all measured at 550 nm, for a window in a building or
a car (e.g., a sunroof) is preferably in the range of from about
(the difference (T.sub.c1 %-T.sub.c2 %) as in FIG. 35) 0.1% to
about 20%, more preferably from about 1% to about 15%, and most
preferably from about 5% to about 10% from the desired colored
state. The above transmission criteria can also be used where the
devices only color in the near infrared region, about 0.7 .mu.m to
about 2.5 .mu.m. The change in light transmission can be solar
transmission instead of photopic transmission. Furthermore, the
light transmission wavelength can be selected in any conveniently
selected range.
The process of this invention is explained referring to FIG. 35,
where transmission vs. time and applied voltage vs. time is plotted
for a typical EC device controlled by the present invention. A
voltage V.sub.C is first applied to colored the window (as shown by
the transmission T % falling, indicating that the light
transmission is low). The voltage is then removed, as shown by a
break in the voltage line, for a period of t.sub.1. During this
time t.sub.1, the cell starts to bleach, as shown by the
transmission T % rising. The time t.sub.1 is related to the length
of the color state memory for a particular EC device. To keep a
window colored (after initial coloration), the coloring potential
is reapplied for a period of t.sub.2 followed by the removal of
power (holding period) for a period of t.sub.1. This alternating
sequence is continued indefinitely, for as long as it is desired to
keep the device in that desired state of transmission. The desired
state is a range of transmission defined by T.sub.c1 % and T.sub.c2
%. In this case, the total time t.sub.c is the overall time of
coloration.
FIG. 35 also shows that the initial coloring voltage can be applied
as an increasing linear ramp to a maximum potential V.sub.C.
Alternatively, a step potential V.sub.C can be applied. Another way
to apply the potential is by imposing a maximum current limitation.
Either of these two modes, or a non-linear ramp, could be
conveniently used. With increasing device area, it may be preferred
to ramp the coloring and bleach potential so that the current
densities at the edges can be lower. This also promotes a spatial
uniformity in color change during coloration and bleaching. This is
particularly noticeable as the device area increases. Also during
the interval t.sub.2, the coloration potential (V.sub.C) could be
applied as a step potential (as shown), or it may be ramped from
the open circuit potential of the device to V.sub.C. It must be
noted that V.sub.C or V.sub.b referes to the potential which the
power supply attempts to apply to the EC cell and is also the
limiting potential on the EC cell. Hence the EC cell has
charateristics of an (RC) circuit, the potential of the cell
(V.sub.cell) only changes slowly as shown by the dashed line in
FIG. 35.
One of the more important variables that affects t.sub.1 and
t.sub.2 is the device temperature. As an example, depending on the
EC device and the components used, t.sub.1 at -20.degree. C. could
range from a few hours to several days or even months, while
t.sub.1 at 70.degree. C. could change to range from about 1 to
about 15 minutes. Similarly, t.sub.2 at -20.degree. C. could range
from about 1 to about 60 minutes, while changing to range at
70.degree. C. from a fraction of a minute to about 10 minutes.
Further, the change in these times might not be linear with
temperature.
It is understood that for certain situations, t.sub.1 and t.sub.2
can be fixed as in the prior art; but in this invention these time
intervals can be allowed to change as discussed above, unlike the
prior art.
FIG. 35 also shows that even the bleach time (t.sub.B) could depend
on the device temperature or/and on the total time the device was
kept in the colored state (t.sub.C) prior to initiating the
bleach.
Typically both t.sub.1 and t.sub.2 decrease with increasing
temperature. Thus, incorporation of a temperature sensor which
provides a feedback into the control circuit could be used for this
purpose. The temperature sensor may be any convenient sensor such
as, for example, a thermistor, a RTD thermocouple, a transistor, or
a diode, the output from which can be used to determine t.sub.1 and
t.sub.2.
For example, referring to FIG. 36A, in the case where a timer is
used to provide the t.sub.1 and t.sub.2 circuit functions, the
thermistor would preferably be a negative thermal coefficient (NTC)
thermistor. When the temperature increases, the resistance of the
NTC thermistor would decrease and the resulting RC product (R is
resistance, and C is capacitance) connected to the LM 556 (National
Semiconductor, Santa Barbra, Calif.) timer would also decrease
leading to smaller t.sub.1 and t.sub.2. The drop in resistance in
the NTC thermistor with temperature would be correlated with the
transmission changes during t.sub.1 and t.sub.2 periods of the EC
device.
Preferably, the temperature coefficient of the thermistor and the
capacitor in the circuit should be chosen so that the change in RC
would naturally mimic the desired change trends needed for t.sub.1
and t.sub.2. One may even employ two thermistors in conjunction
with two capacitors respectively, where the parameters of one set
of resistors/capacitors are tailored to correspond with the changes
in t.sub.1 and the other set of resistors/capacitors corresponds
with the changes in t.sub.2.
In a variable coloration device, t.sub.1 and t.sub.2 will depend on
the depth of coloration. For example, in the open circuit mode the
transmission change for a deeper colored state may be faster (thus
requiring a shorter t.sub.1) than for a shallower colored state.
Similarly, it may take more time to achieve a darker state (thus
requiring a longer t.sub.2) Since the depth of coloration is
typically related to the potential used for coloration, one could
define and store in the control circuit a profile of t.sub.1 and
t.sub.2 values that are calibrated with the applied coloration
voltage.
As the device ages, t.sub.1 and t.sub.2 may also shift. Account
could be kept of the number of cycles, time spent in a particular
state of transmission or any other convenient method which keeps a
track of the age and usage of the cell. An aging profile with
varying t.sub.1 and t.sub.2 could be used to drive the cell and if
needed, the potential can also be varied and controlled to keep the
initial level of coloration. Such control can be by any convenient
method such as, for example, the use of monitoring sensors and
feedback processes.
In another aspect of this invention, no prescribed periods are used
but rather the actual level of coloration is sensed through the EC
cell. In this case where one or more photosensors are used, the
degree of color change can be detected by the photosensor and once
the coloration has changed to a predetermined level, the necessary
voltage can be applied to recolor the EC cell back to its original
depth. Use of the photosensor can also eliminate any need to
pre-program values of or factors to calculate t.sub.1 and t.sub.2
with aging, temperature or coloration voltage.
Photosensors, e.g., CdS photoconductors on Si photodiodes, can be
used to provide feedback signals for controlling t.sub.1 and
t.sub.2 instead of presetting fixed values for t.sub.1 and t.sub.2.
In this case, the photosensor(s) would monitor the transmission of
the EC cell and actively signal the circuitry as to the appropriate
times to remove and to apply the voltage. As coloration rates and
bleach rates change with temperature, aging, and other factors,
t.sub.1 and t.sub.2 are adjusted accordingly. Preferably a pair of
photosensors are used. One photosensor is placed on top of the cell
to obtain the baseline for incoming light while another is placed
underneath the cell to collect the transmitted light. The
electrical signals from these two photosensors are then connected
to a differential amplifier, the output of which is proportional to
the relative transmission through the cell. Depending on the sensed
output, the cell will be subjected to open circuit (holding period
t.sub.1) or voltage application (period t.sub.2).
Further, as the cell ages thereby affecting its coloring and
bleaching kinetics, the depth of coloration can still be maintained
since t.sub.1 and t.sub.2 will change due to the feedback provided
by the photosensors. For example if the coloration rate of the cell
slows down, both t.sub.1 and t.sub.2 will increase to maintain a
pre-determined differential output from the photosensors for
identical illumination conditions. Also, if t.sub.1 and t.sub.2
become longer than pre-determined "acceptable periods", then the
circuit may be configured to increase the coloration potential
(subject to a maximum safe-potential for the devices) to increase
the coloration speed.
Another method monitors the current (I) or the rate of change in
current injected with time (t), i.e. dI/dt. Once dI/dt reaches a
prescribed low value, the coloring potential is removed.
The transmission change during the holding period (t.sub.1) can
also be correlated to the open circuit potential change between the
two cell electrodes. During the holding period (t.sub.1), the
potential between the two opposing electrodes of the EC cell
(V.sub.cell) will also decrease. Once a predetermined change in
this voltage (.DELTA.V) is reached, a coloring voltage can be then
applied to recolor the EC device. The time period t.sub.2 can be
determined by checking the current being injected into the cell.
For example, as shown in FIG. 34B, for a constant voltage the rate
of change of the current decreases with time and reaches a limiting
value. Thus, when the change in the current with time becomes
smaller than a predetermined level, the coloring voltage can be
removed.
Alternatively instead of monitoring dI/dt, just the current (I)
could be measured. Once the absolute value of the current is below
a predetermined limit the coloring voltage is removed. As described
earlier, this method also self compensates for any changes in cell
kinetics, caused by aging, by increasing time periods t.sub.1 and
t.sub.2 during the coloration period. When these time periods
become longer than pre-determined "acceptable periods", the circuit
if desired may be configured to increase the coloration potential
(subject to a maximum safe potential for the devices) in order to
increase the coloration speed.
Alternatively, the charge injected during coloration can be
monitored by a charge integration circuit. Once a predetermined
charge has been injected, the coloration voltage can be removed.
For many EC devices, the charge passed into the device for a
desired level of coloration may depend on temperature. One method
to take into account where this charge will increase with
temperature is to have a comparator with a thermistor-containing
reference. All of the control parameters which determine t.sub.1
and t.sub.2 such as T.sub.c1 %, (T.sub.c1 %-T.sub.c2 %), .DELTA.V,
I, and dI/dt may be fixed and/or varied with temperature and/or
aging of the device. One may also determined ti or t.sub.1 by
measuring the voltage at the EC cell V.sub.cell and comparing this
with the V.sub.C or V.sub.B. During coloration V.sub.cell
asymptotically approaches V.sub.C. When V.sub.cell is within 5%
(preferable 1%) of V.sub.C, the coloring potential V.sub.C is
removed to let the cell rest in open circuit conditions.
Alternatively, V.sub.C could be continued to be applied for an
additional fixed time after the above condition is met to allow the
cell to reach equilibrium. The total coloration time (t.sub.1 or
t.sub.2) are obtained by adding the time for coloration during
which V.sub.cell approaches V.sub.C and the fixed duration
described above. During the open circuit mode (e.g., in coloration)
the potential of the cell (V.sub.cell) is measured and when it
drops to about 3 to 30% of V.sub.C (preferably 10 to 15% of
V.sub.C) the coloring voltage V.sub.C is re-applied. Schematically
an electric circuit showing V.sub.cell and V.sub.C (or V.sub.B) is
shown in FIG. 45.
In addition to varying t.sub.1 and t.sub.2 with temperature, the
coloring and bleaching voltages may also be varied with temperature
if desired. For example, depending on the devices, higher voltages
may be used at lower temperature or vice-versa. Additionally, with
temperature feedback to the control circuitries, both the duration
(i.e., t.sub.1 and t.sub.2) and the voltage can be varied
simultaneously to further mitigate electrical or electrochemical
stress on the EC cell.
The voltage can be made temperature dependent by having a
thermistor-containing voltage reference in the power supply. This
thermistor can be a NTC (negative thermal coefficient) or a PTC
(positive thermal coefficient) type. As the temperature rises the
resistance will be lower in NTC thermistors. Consequently, when
incorporated with suitably-biased series resistors and an
operational amplifier (op amp), the reference voltage to the
error-sensing op amp will be lower as temperature increases,
resulting in a lower voltage applied to the EC cell at higher
temperatures.
An example of a circuit incorporating an NTC thermistor TM1 and an
op amp OP1 is shown in FIG. 39. As the temperature increases, the
resistance of the TM1 will be lower, resulting in a reference
voltage from PS2 to OP1 to be lower. Thus, output voltage V.sub.out
will be lower. Accordingly, a properly designed resistor stack with
a combination of series and/or parallel resistors incorporating
such thermistors would cause the voltage needed (V.sub.out) to
track with operating temperature. In a particular example, the
values of each component were: PS1 was 12 VDC, R1 and R2 were 10
K.OMEGA. each, C1 was 10 .mu.F, PS2 was 2.5 VDC, OP1 was a LM324 op
amp available from National Semiconductor, Santa Clara, Calif., TM1
was an NTC Thermistor having a resistance of 1.76 k.OMEGA. at
50.degree. C., and the output voltage was 1.35V.
A PTC thermistor TM2 can also be used in a circuit to change the
output voltage with temperature, an example of which is shown in
FIG. 40. In a particular example, the values of each component were
similar to that example above, PS3 was 12 VDC, R3 and R4 were 10
K.OMEGA. each, C2 was 10 .mu.F, PS4 was 2.5 VDC, OP2 was a LM324 op
amp, TM1 was an PTC Thermistor having a resistance of 1.76 K.OMEGA.
at 50.degree. C., and the output voltage was 1.15 volts.
Additionally, the thermistor can also be used in a comparator
circuit to trigger the microprocessor to use different t.sub.1, and
t.sub.2 periods, for example, as shown in FIG. 41. In the example,
the thermistor TM3 used was a NTC Digikey part # PNT 117-ND
available from Panasonic, Cupertino, Calif., with a resistance of
1.76 K.OMEGA. at 50.degree. C. The potentiometer resistor R5 in
series with the thermistor was adjusted to match the thermistor's
set value, i.e. 1.76 K.OMEGA.. PS5 was 12 VDC, R6 and R7 were each
15 K.OMEGA., and the op amp was an LM324 op amp available from
National Semiconductor. As a result, the voltage drop across R6 and
R7 (Vcc) is 5.0V. The positive input of the op amp is fixed at 2.5V
by the two 15 K.OMEGA. series resistors R6 and R7. At temperatures
lower than 50.degree. C., the TM3 resistance is higher than 1.76
K.OMEGA. resulting in a voltage of higher than 1/2 of Vcc (that is,
2.5V) to the negative input of the LM324 op amp. Since the negative
input is higher than the positive input there is no output from the
op amp at such lower temperatures. When the temperature climbs to
50.degree. C. and above, the resistance in the thermistor drops
below 1.76 K.OMEGA., thereby lowering the voltage below 2.5V and
resulting in a positive output signal from the op amp that can be
routed to a microprocessor input port. The microprocessor can then
change the t.sub.1, and t.sub.2 periods in response to the positive
output signal.
Based on this circuit, the output of the op amp will be turned on
at the threshold temperature; however near the region of this
threshold there may be thermal fluctuations which may cause the
output to erratically turn on and off. In order to eliminate such
erratic behavior, a positive hysteresis can be added to the op amp
comparator using positive feedback. As shown in FIG. 42, a feedback
loop can be formed by resistor R12, resulting in a Schmitt trigger.
In the example, the values of the components were those of the
corresponding components in FIG. 41, with the added resistors R11
being 10 K.OMEGA. and R12 being 1 K.OMEGA..
With such a Schmitt trigger in the circuit, the low trigger
threshold is different from the high trigger threshold (the
difference being the hysteresis intentionally induced in the
comparator, rather than a single threshold value as in a
conventional comparator). Such Schmitt triggers can also be used in
photosensors to detect daylight--it is well known that around the
region of daylight threshold, e.g., during dusk and dawn,
photocells can behave erratically. Having positive hysteresis in
the op amp comparator will aid in obtaining a smooth output.
Furthermore, Schmitt triggers can be used in EC skylight circuits
where both photosensors and temperature sensors are employed.
FIG. 43 shows an example of an implementation of an adjustable
voltage power supply where the output voltage supplied to the
electrochromic panel ECU1 can be tuned to give two different output
voltages depending on the transistor switch T4 which will be
activated when there is a predefined temperature change. In a
particular example, PS7 was 12 VDC, PS8 was 2.5 VDC, R14 and R13
were each 10 K.OMEGA., R15 and R16 were each 1 K.OMEGA., R17 was 4
K.OMEGA., and C3 was 10 .mu.F. The transistors T3 and T4, and the
op amp were those described above. The trigger to the base of T4
can come from either a microprocessor port as shown in FIG. 43, or
the comparator output from a circuit as shown in FIG. 41 or 42.
Upon turning on of transistor T4, the resistor R15 will be in
parallel with the reference resistor R14 resulting in a lower
overall resistance and hence lower reference voltage to the
error-sensing op amp. The output voltage will also be lower.
Alternatively, such output voltage can change to vary the EC color
voltage below full coloration, e.g., during half color.
The EC power supply can also incorporate current limitation, e.g.,
using simple transistor switching or current holdback techniques.
The addition of a sensing resistor in series with the power output,
together with another transistor as shown in FIG. 44, can limit the
maximum current flowing in the circuit by the judicious choice of
the sensing resistor R20 value. This sensing resistor can be fixed
for constant maximum current or made variable for variable current
limiting in the circuit. In a particular example, PS9 was 12 VDC,
PS10 was 2.5 VDC, R18 and R19 were 10 K.OMEGA., TM4 was an NTC
thermistor having a resistance of 1.76 K.OMEGA. at 50.degree. C.,
Op Amp OP6 was an LM324, T5 and T6 were 2N3904 transistors
described above, and C4 was 10 .mu.F. With sensing resistor R20
having a resistance of 1 K.OMEGA. (V.sub.BE of T6 is 0.7 volts),
the voltage output V.sub.OUT was 1.35 volts, and was limited to a
current I.sub.OUT of 0.7 mA.
A particular benefit of this current limiting is in the case of an
electrical short - the circuit will allow only the maximum limited
current to flow through rather than a potentially damaging high
current, thus offering protection.
In some devices, the variation in t.sub.1 may be much more strongly
dependent on temperature than t.sub.2 (e.g., see device #1 and 2 in
Table 5 below). In such cases the powering circuit could be
simplified so that only t.sub.1 varies with temperature and t.sub.2
is fixed in duration.
In all the examples above it is assumed that the coloration and
bleaching are controlled by applying a pre-specified maximum
potential and that this potential can be a step, ramp, non-linear,
etc. In another method the power supply can be configured so that
it applies a pre-specified current for coloring and bleaching,
subject to a maximum safe-potential. This means that the applied
potential from the power supply will vary with time (to compensate
for changes in impedance, for example).
In coloration, as an example, a controlled current source could be
used. The current is reduced, or the current source is removed, as
the maximum safe-potential is reached. Thus, when a pre-specified
potential between the cell electrodes is reached, the power source
is removed. A current limit for coloring (or bleaching) for
non-internal busbar cells is typically chosen between 50 to 5000
.mu.A/cm.sup.2 of active area of the EC cell, more preferably
between 100 and 1000 .mu.A/cm.sup.2. For cells with internal
busbars current limit (if imposed) can exceed the upper limit of
this range to insure that time to color and bleach is rapid.
In all cases where the temperature is being measured, it is
important that the temperature measuring or sensing elements such
as thermistors, ferroelectric capacitors, thermocouples, or other
such temperature measuring means, are mounted in such a way that
they sense or measure temperatures that are similar to the
temperature of the EC cells. That is, the measured temperature must
have a corresponding relation to the temperature of the EC cell.
For example, the measuring means could be mounted on a cell
surface, on a cell edge, or at a position proximate to the cell so
that the temperature of the cell and the temperature of the sensing
element are similar. In some cases it may be preferred to mount the
thermistor so that it is hidden from the direct view of the user.
Adhesives with high thermal conductivity may be used for mounting
so that the sensing elements are close in temperatures to the
substrates they are mounted on.
In other examples where the EC cell is large, or where the sensing
element controls multiple EC cells, it is apparent that the sensing
element should measure a temperature that is relevant to the
temperature of the large EC cell or of the multiple EC cells. Such
relevant temperature would be, for example, an average temperature
across the large EC cell or the multiple EC cells. In other cases,
the peak or low temperature might be relevant. Accordingly, the
sensing element should be positioned so that such a relevant
temperature is sensed or measured.
The above descriptions of determining t.sub.2 may also be used for
determining and/or controlling t.sub.1. The time period t.sub.b may
be fixed or could be varied.
The Examples which follow are intended as an illustration of
certain preferred embodiments of the invention, and no limitation
of the invention is implied.
Example 16 with Thermistor and/or Ferroelectric Capacitor
Referring to FIG. 36A, the EC control circuit was designed to
incorporate the intermittent powering of the EC cell E1, as
described above. In this example, the coloring and bleach
potentials were fixed at 1.2 V and -3V respectively, while t.sub.1
and t.sub.2 were allowed to vary with temperature.
The system can utilize any convenient voltage as would be apparent
to one of ordinary skill in the art. In this case, for example, 12V
DC is used. The voltage can be supplied from any convenient source
such as, for example, from a car battery or from a transformer that
steps down 110V AC to 12V DC. The circuit uses a LM 556 dual timer
(National Semiconductor, Santa Clara, Calif.), which includes an
astable timer U1/A and a monostable single shot timer U1/B, to
control the timed cycles for the EC device.
Astable timer U1/A includes an RC circuit comprised of resistors
R2, R3, and capacitor C1. This astable timer provides the holding
and voltage application periods. The periods for t.sub.1 and
t.sub.2 are obtained by using the formula t.sub.1 =0.693(R3+R2)C1
and t.sub.2 =0.693(R2)C1. The output of timer U1/A drives a
transistor Q1 which then further drives a transistor Q2. Transistor
Q2 activates the relay K1:A which upon closing applies the coloring
potential from the 1.2V voltage source.
A pair of diodes D1 and D2 isolate the outputs of U1/A and U1/B
from each other. Astable timer U1/A is cycling constantly but its
output is only applied to electrochromic cell E1 when switch S3 is
in the color position after an initial time period, for example,
200 sec from U1/B.
Resistors R2 and R3 may each be replaced with a NTC thermistors,
e.g., model DC95-& 104Z available from Thermometrics, Edison,
N.J., to allow for t.sub.1 and t.sub.2 compensation at
electrochromic cell E1. For example, the cycling conditions of a
particular EC device at 25.degree. C. are t.sub.1 =138 sec, t.sub.2
=69 sec. These times are obtained with thermistor R2 and R3 values
of 100 K.OMEGA. and C1 of 1 mF. Using the thermistors described,
the resistance increases to 1 M.OMEGA. at -25.degree. C. and
decreases to 23 K.OMEGA. at 65.degree. C., resulting in t.sub.1
=1444 sec and t.sub.2 =722 sec at -25.degree. C., and t.sub.1 =32
sec and t.sub.2 =16 sec at 65.degree. C., respectively.
Monostable single shot timer U1/B provides the initial duration--in
this case, for example, 200 sec, of coloring or bleaching
potential. The duration for the initial color (t.sub.i) or bleach
(t.sub.b) is calculated according to the formula t=R3*C4. The
values are calculated, in this example, to yield the 200 sec
duration to initially color or bleach the cell and is triggered by
switch S1. The output from switch S1 drives transistors Q2 and Q3.
Resistor R6 can be replaced with an NTC thermistor to obtain longer
and shorter initial bleaching (or coloring) periods,
respectively.
The potential which is applied to electrochromic cell E1 depends on
the position of switch S3, which the user selects. If switch S3 is
in the coloring position, astable timer U1/A takes over after the
initial 200 sec coloring cycle and then electrochromic cell E1 is
cycled intermittently by astable timer U1/A to maintain coloration.
Astable timer U1/A is never applied while switch S3 is in the
bleaching position.
Alternatively, ferroelectric-capacitors having a Curie point,
T.sub.c, for example, below -45.degree. C., based on SrTiO.sub.3
-containing compositions, can also be used in the timer circuit to
provide temperature sensitive capacitors. In these capacitors, the
capacitance declines with increasing temperature. Accordingly, such
capacitors can be used to cause the periods of t.sub.1 and t.sub.2
to be changed along non-linearly with temperature changes, such as
to cause even longer periods at lower temperatures and shorter
periods at higher temperatures. Furthermore, a combination of
thermistors and ferroelectric capacitors can be used simultaneously
to obtain the RC product necessary to change t.sub.1 and t.sub.2
according to temperature.
A microcontroller can also be used to obtain t.sub.1 and t.sub.2
functionalities in the control circuitries using built-in timer
modes thus negating the use of any external timer chips such as
LM555 or LM556. Examples of such microcontrollers are PIC16F84 from
Microchip (Chandler, Ariz.), MC68HC11E9 from Motorola (Tempe,
Ariz.), and Z-80 from Zilog (Campbell, Calif.). Temperature sensors
can be connected to the microcontroller to change t.sub.1 and
t.sub.2 accordingly. Flash memory or EEPROM can further be utilized
in conjunction with the microcontroller to store information on the
temperature dependence, electrical history and aging properties of
the EC cell. This information will then be used as feedback to
optimize the cell bleaching and coloring characteristics. These may
include changes to V.sub.c, V.sub.b, T.sub.c1 %, T.sub.c2 %,
t.sub.i, t.sub.1, t.sub.2 and t.sub.b.
In a particular example, a Microchip microcontroller PIC16F84 as
shown in FIG. 36B was used (in place of the LM 556 dual timers of
FIG. 36A) in a circuit similar to that shown in FIG. 36A. The EC
cell was configured so that it could only be colored during the day
time by using a CdS photocell sensor to determine whether it is
daytime or nighttime. At night, the EC coloring function was
disabled. Upon coloring, a coloring potential of 1.2V from the
power supply would be applied to the cell for 3 minutes. Following
this initial coloring potential, the specific t.sub.1 and t.sub.2
intermittence functionality (for example, 45 sec turn off and 15
sec turn on of the coloring potential) was also written into the
program. Upon bleaching, a -0.3 V would be applied to the cell for
3 minutes. During the coloring or bleaching process, the output pin
would be enabled turning on the relay or semiconductor switches to
power the EC cell directly from the coloring or bleaching power
supplies. The firmware was programmed into the microcontroller
using a PicStart Plus Programmer. A thermistor suitably mounted on
the EC cell can also be connected to one of the I/O ports in the
P1C16F84. The change in resistance of the thermistor is then
correlated to temperature of the EC cell. Depending on the
temperature measured, the coloring and bleaching potentials,
t.sub.1 and t.sub.2 characteristics can then be controlled.
Microcontrollers can also be used to control the powering method of
the EC cells during coloring and bleaching. This includes specific
potential ramps, constant current control, or potential increases
and decreases in multiple discrete steps.
Example 17
Change in t.sub.1 and t.sub.2 with Temperature of Electrochromic
Devices
Various electrochromic devices, 3 in.times.3 in, were fabricated
using 12 ohms/square ITO as the conductive substrates. The tungsten
oxide coating deposition methods and device fabrication processes
used in these EC devices were similar to the methods and processes
described in copending U.S. patent application Ser. No. 09/155,601
(incorporated by reference herein) which also describes the use of
and methods to fabricate Selective Ion Transport Layers (SITL). The
EC devices were made both with SITL layers and without SITL layers.
The electrolyte consisted of at least one solvent, one dissociable
salt and at least one redox promoter. Polymeric viscosity modifiers
and UV stabilizers and water were also added.
Although any of the solvents described in copending U.S. Pat.
Application Ser. No. 09/155,601, could be used, although
carbonates, sulfolanes, glymes, and their mixtures are preferred.
Examples of suitable carbonates are propylene carbonate, ethylene
carbonate, ethyl propyl carbonate, isopropyl ethyl carbonate,
diethyl carbonate, methyl propyl carbonate, isopropyl methyl
carbonate, ethyl methyl carbonate, dimethyl carbonate, butylene
carbonate and other alkyl carbonates. Examples of some other
suitable solvents are alkyl sulfones, tetraglyme, toluene, xylene,
decaline and other aliphatic and aromatic alkyls with or without
substituted polar groups.
Dissociable salts were typically based on alkali metal cations,
such as lithium, sodium, and potassium. Some examples of suitable
anions are perchlorate, tetrafluoroborate, triflate, etc., as
described in copending U.S. patent application Ser. No. 09/155,601,
which lists other suitable salts.
When tungsten oxide, molybdenum oxide and other cathodic oxides and
their mixtures were used as chromogenic layers, the redox promoters
used in the devices were typically based on ferrocene and its
derivatives. Substituted ferrocenes with electron donating groups
attached on the cyclopentadiene rings of the ferrocenes are a
preferred sub-class in ferrocenes. These groups can be substituted
to any of the cyclopentadiene rings. Further, the substituted
groups may be the same or different on each of the rings. Such
groups include methyl, propyl, n-butyl, tertiary butyl, etc.
Examples of such ferrocenes include decamethyl ferrocene,
octamethyl ferrocene, tertiary butyl ferrocene, interannual
substituted ferrocenes such as 1-1'-(propane-1,3-diyl) ferrocene,
1,1':3,3'-bis(propane-1,3-diyl) ferrocene,
1,1':2,2':4,4'-tri(propane-1,3-diyl) ferrocene. Another preferred
sub-class of ferrocenes are biferrocenes and bridge ferrocenes,
where in the latter, the cyclopentadiene rings of different
ferrocene molecules are chemically bonded to each other. Examples
of these include 2,2-bis(tert-butylferrocenyl)propane,
2,2-bis(ethyl ferrocenyl)propane, etc. Further, the selection of
the ferrocene will also influence the extent of the back reaction
with other ingredients, components and device construction details
remaining the same.
Typically, inclusion of polymers that are soluble in the
electrolyte will result in increased viscosity and accordingly such
polymers can be used as viscosity modifiers.
The size of such crystals should typically be smaller than about
0.5 .mu.m, preferably less than 0.2 .mu.m so that they do not
create haziness in optically clear systems. Some preferred polymers
are polymethyl methacrylate, polyvinyl chloride, polyvinyl chloride
and polyvinyl acetate copolymers, polyvinyl butyral,
polyacrylonitrile and its copolymers, polyvinylidene fluoride,
copolymers of polyvinylidene fluoride and hexafluoropropylene. The
last two are available from Elf Atochem North American
(Philadelphia, Pa.) under the trade names of Kynar and Kynar flex
respectively.
In one of the samples the electrolyte was processed using a sol-gel
technique to form a solid. The solid resulted from the formation of
"Si--O--Si" cross-linkages in-situ after filling the EC cell with a
electrolyte precursor. This is also described below.
The selection and the concentration of the ingredients described
above will influence the extent of the back reaction while other
components and device construction details remain the same. The
back reaction will change with temperature and this will cause
change in t.sub.1 and t.sub.2.
As shown in Table 5 below, the presence and absence of a SITL
layer, the type of SITL layer, and any changes in the electrolyte
have considerable influence on t.sub.1 and t.sub.2. Polyceram SITL
layer formation by sol-gel processing is described below.
Polystyrene-sodium-sulfonate (PSSNa) SITL layer was processed by
dip-coating the tungsten oxide coated substrates with a 540,000
mol. wt. PSSNa solution (5% by weight/vol) in a 50/50 mixture (by
volume) of distilled water and reagent grade ethanol and 0.01% of a
surfactant, Triton X-100 available from Aldrich Chemical Co.
(Milwaukee, Wis.).
The devices were colored by applying 1.2V. The values of T.sub.c1 %
and T.sub.c2 % (FIG. 35) were 10% and 15% respectively. The leakage
current was measured as the current consumed after applying the
coloring potential for 15 minutes. The table also shows that when
ferrocene has bulky constituents, such as in the compound
2,2-bis(ethyl ferrocyl)propane, a lower leakage current is
obtained. For example, compare the leakage current of device 1 to
that of device 2, and the leakage current of device 5 to that of
device 6.
The various elecctrolyte compositions were:
Electrolyte A: 85% Propylene carbonate, 0.8% 2,2-bis (ethyl
ferrocenyl) propane, 0.4% LiClO.sub.4, 9.4% PMMA, 3.6% UV400, and
0.1% water (all percentages by weight).
Electrolyte B: 85.2% Propylene carbonate, 0.7% ferrocene, 0.4%
LiClO.sub.4, 9.5% PMMA, 3.6% UV400 and 0.7% water (all) percentages
by weight).
Electrolyte C: 53.6% Propylene Carbonate, 35.7% Sulfolane, 8.4%
Poly(methyl methacrylate), 1.0% Dionized water, 0.8% Ferrocene,
0.5% Lithium perchlorate (all percentages by weight).
TABLE 5 Leakage Device Electrolyte SITL Type of Temp. t.sub.1
t.sub.2 current # composition Layer SITL layer .degree. C. (s) (s)
(.mu.A/cm.sup.2) 1 Electrolyte C No 25 30 20 210 50 20 20 370 70 15
20 530 2 Electrolyte A No 25 61 6 126 50 31 4 268 70 24 4 392 3 See
formation of No 25.sup.a 7 31 29 sol-gel electrolyte .sup. 50.sup.b
5 15 87 below this table 70.sup.c 2 12 151 4 Electrolyte B Yes
Polyceram-2 25 1079 14.4 6.4 50 431 7.2 31.5 70 184 5.8 90.0 5
Electrolyte B Yes Polyceram-1 25 590 24 10 50 145 8 47 70 64 6 136
6 Electrolyte A Yes Polyceram-1 25 2749 10.2 4.8 50 1272 6 13 70
785 4 26.7 7 Electrolyte C Yes PSSNa 25 3600 25 3.3 70 900 7 14.5
.sup.a T.sub.c1 % and T.sub.c2 % were 18.8% and 23.8% respectively
.sup.b T.sub.c1 % and T.sub.c2 % were 23.3% and 28.3% respectively
.sup.c T.sub.c1 % and T.sub.c2 % were 30% and 35% respectively
Example
Formation and Processing of Polyceram-1 SITL Layer (CH.sub.3
(OCH.sub.2 CH.sub.2).sub.n OCONH(CH.sub.2).sub.3 Si(OC.sub.2
H.sub.5).sub.3 /Si(OCH.sub.3).sub.4, Overcoated on WO.sub.3
electrode)
Polyceram layer was processed as described in the examples given
below. Polyceram layer was made in the same way but the ratio of
ingredients was modified. The weight ratio of (CH.sub.3 (OCH.sub.2
CH.sub.2).sub.n OCONH(CH.sub.2).sub.3 Si(OC.sub.2 H.sub.5).sub.3 to
Si(OCH.sub.3).sub.4 was 1:0.51 in the case of Polyceram-1 but
1:1.02 in the case of Polyceram-2.
75.00 g of poly(ethylene glycol) methyl ether, CH.sub.3 (OCH.sub.2
CH.sub.2).sub.n OH (number average MW=ca. 350, obtained from
Aldrich Chemical Co., Milwaukee, Wis.), 58.31 g of
3-(triethoxysilyl) propylisocyanate, (C.sub.2 H.sub.5 O).sub.3
Si(CH.sub.2).sub.3 NCO, and 0.15 ml of dibutyltin dilaurate were
heated at approximately 50.degree. C. under nitrogen, with
stirring, for 2 hrs to give a silylated derivative with the nominal
formula: CH.sub.3 (OCH.sub.2 CH.sub.2).sub.n OCONH(CH.sub.2).sub.3
Si(OC.sub.2 H.sub.5).sub.3.
24.30 g of CH.sub.3 (OCH.sub.2 CH.sub.2).sub.n
OCONH(CH.sub.2).sub.3 Si(OC.sub.2 H.sub.5).sub.3, 49.59 g of
C.sub.2 H.sub.5 OH and 2.20 g of H.sub.2 O (acidified to 0.15M HCI)
were combined and refluxed for 30 mins. The solution was then
cooled and 12.38 g of Si (OCH.sub.3).sub.4 added and the resulting
solution refluxed for 60 mins. The solution was then cooled and
5.86 g of H.sub.2 O (acidified to 0.15M HCl) was added and the
resulting solution refluxed for 60 mins. The solution was then
cooled and 3.00 g of Amberlyst.RTM. A-21 ion-exchange resin (Rohm
& Haas Co.) added, followed by gentle stirring. After 30 mins
the solution was filtered through a fritted glass disc Buchner
funnel. 45.00 g of the filtrate was taken and 0.21 g of
3-aminopropyltriethoxysilane was added. The resulting solution was
diluted 1:1 (by weight) with ethanol and filtered through a 1 .mu.m
syringe filter. It was then spin-coated on a transparent WO.sub.3
ITO coated glass substrate. The coating was cured at 135.degree. C.
for 1 hr under humid atmosphere, after this treatment it has a
thickness of about 0.6 .mu.m. A device was then assembled as
described in Comparative Example 1.
Example
Formation and Processing of Polyceram-2 SITL Layer (CH.sub.3
(OCH.sub.2 CH.sub.2).sub.n OCONH(CH.sub.2).sub.3 Si(OC.sub.2
H.sub.5).sub.3 /Si(OCH.sub.3).sub.4 overcoated on WO.sub.3
electrode)
6.08 g of (CH.sub.3 (OCH.sub.2 CH.sub.2).sub.n
OCONH(CH.sub.2).sub.3 Si(OC.sub.2 H.sub.5).sub.3, 12.40 g of
C.sub.2 H.sub.5 OH and 0.55 g of H.sub.2 O (acidified to 0.15M HCl)
were combined and refluxed for 30 mins. The solution was then
cooled and 6.19 g of Si (OCH.sub.3).sub.4 added and the resulting
solution refluxed for 60 mins. The solution was then cooled and
2.93 g of H.sub.2 O (acidified to 0.15M HCl) was added and the
resulting solution refluxed for 60 mins. the solution was then
cooled and 1.30 g of Amberlyst.RTM. A-21 ion-exchange resin (Rohm
& Haas Co.) added, followed by gentle stirring. After 30 mins
the solution was filtered through a fritted glass disc Buchner
funnel. The filtrate was diluted 1:2 (by weight) with ethanol and
filtered through a 1 .mu.m syringe filter. It was then spin-coated
on a transparent WO.sub.3 ITO coated glass substrate. The coating
was cured at 135.degree. C. for 1 hr under a humid atmosphere,
after this treatment it had a thickness of 0.3 .mu.m. A device was
then assembled as described in Comparative Example 1.
Example
Formation of Sol-gel Electrolyte
This describes a crosslinkable electrolyte which can be substituted
for the electrolyte in cells such as those given in Comparative
Example 1a or in other examples with SITL overlayers described
earlier. The electrolyte was prepared in the following way: 12.00 g
of poly(ethylene glycol). HO(CH.sub.2 CH.sub.2 O).sub.n OH (number
average molecular weight=ca. 400, obtained from Aldrich Chemical
Company), 15.58 g of 3-(triethoxysilyl) propyl isocyanate, (C.sub.2
H.sub.5 O).sub.3 Si(CH.sub.2).sub.3 NCO (obtained from Aldrich
Chemical Company), and 0.03 g dibutyltin dilaurate, (CH.sub.3
(CH.sub.2).sub.3).sub.2 Sn(O.sub.2 C(CH.sub.2).sub.10
CH.sub.3).sub.2, were heated to approximately 70.degree. C. under
nitrogen, with stirring, for 15 minutes to yield a silylated
derivative with the nominal formula: (H.sub.5 C.sub.2 O).sub.3
Si(CH.sub.2).sub.3 HNOC(OCH.sub.2 CH.sub.2).sub.n
OCONH(CH.sub.2).sub.3 Si(OC.sub.2 H.sub.5).sub.3.
2 g of CH.sub.3 (OCH.sub.2 CH.sub.2).sub.n OCONH(CH.sub.2).sub.3
Si(OC.sub.2 H.sub.5).sub.3, 1.50 g (H.sub.5 C.sub.2 O).sub.3
Si(CH.sub.2).sub.3 HNOC(OCH.sub.2 CH.sub.2).sub.n
OCONH(CH.sub.2).sub.3 Si(OC.sub.2 H.sub.5).sub.3 (prepared as
above), 1.75 g .gamma.-butyrolactone, 0.0326 g ferrocene, and
0.4107 g LiClO.sub.4 are stirred until a clear solution is formed.
Then 0.3636 g H.sub.2 O (acidified to 0.15 M HCl) is added. The
solution is stirred until homogeneous. A cell fabricated as in
comparative Example 1 utilizing an ITO electrode and a transparent
WO.sub.3 ITO coated glass substrate is then filled with the
solution obtained above. The cell thickness in this example was 53
.mu.m rather than 210 .mu.m as given in the earlier example. After
filling the cell, the solution forms a rigid gel (net work) within
10 hours. The gel time can be controlled, e.g., by changing the
type and amount of catalyst (e.g., HCl is used above) as known in
the art, temperature of cell after filling and using appropriate
functionality of the ingredients. Functionalised ferrocenes also
could be used which will attached chemically to the electrolyte
network. Some exemplary ferrocenes are: ##STR1##
These ferrocenes could be used by themselves or in conjunction with
non-functionalized ferrocenes (the ones which will not chemically
attach to the network). Depending on the cell characteristics if
non-ferrocene redox materials are used, the same can be implemented
for non-ferrocene redox materials. The cell may also consist of
ferrocene and non-ferrocene based redox materials.
Power Consumption Reduction in EC Devices by Using Switching Power
Supplies
The power consumption of these devices can be further reduced by
incorporating such elements in the circuit that would efficiently
step down the voltages from the incoming power supply to the
desired coloration or bleaching voltages. For example, a typical
car battery has an output of about 12V, while an EC device might
only need 1 to 2 volts for coloration, for example 1.2V. Thus, if
the EC device needs a current of 10 mA in the colored state at a
voltage of 1.2V, then a power conserving circuit would allow only a
1 mA drainage from the battery at 12V assuming that the power is
converted at 100% efficiency.
Typical power supplies for powering EC devices in automotive
mirrors use linear regulators or linear regulation for the voltage
conversion process. Although widely used for such applications, the
power conversion efficiencies of linear regulators are usually very
low, typically 10-30%. The conversion efficiency, however, is
typically not a major concern. Since the EC mirror is normally
operated when the car in turned on, the current or power draw is
not a significant drain on the car's alternator and linear
regulation can be utilized. Examples of such circuits are described
in U.S. Pat. Nos. 5,148,014, 5,193,029, and 5,220,317, each
incorporated herein by reference.
However, the switching regulator can be used for EC devices as
taught in the present invention and can offer up to 95% efficiency.
In the prior art power supplies, the current draw is usually
maintained when the voltage is switched from high to low potential.
For example, for linear regulators, in going from 12 V at 1 mA, to
1.2 volts, the output current will still be 1 mA, which reflects a
power conversion efficiency of only 10%. In this invention, use of
circuits that regulates the power supply voltage by a switching
function to control the electrochromic products increases the power
conversion efficiency by at least two fold over linearly regulated
power supplies.
In aircraft, boats, eyewear and automotive EC windows, such as
automotive EC sunroofs, where the coloration needs to be maintained
even when the vehicle is in a mode such as when parked, where the
engine is off, the current drain from the battery becomes a
critical issue. In cars, the current draw is usually preferably 2
mA or less at 12V in order not to drain the battery excessively.
During this coloration state, the present invention subjects the
cell to an intermittent voltage rather than a continuous voltage,
thereby enhancing device durability. During initial coloration and
intermittent coloration periods (t.sub.2) the switching power
supply of the present invention is used to convert the power
efficiently to reduce the battery drain. During the holding period
when no current is flowing, the regulator should preferably have a
low or no quiescent current.
An example of a switching regulator circuit used in this invention
is shown in FIG. 37A. The circuit is able to regulate even low
voltages below about 1.2V. As described earlier, the switching
regulator circuit of this invention has a low or no quiescent
current in order not to drain the battery excessively. Switching
regulators, as used here, have lower current drains than linear
regulators. The switching regulator of the present invention
preferably should have a quiescent current drain of lower than 100
mA. It is more preferred that the switching regulator of the
present invention have a quiescent current drain of lower than 25
mA and most preferably lower than 5 mA. Such low current drains
minimize drawdown of the battery in situations where the battery is
not being charged such as while the vehicle is parked with ignition
off.
Comparative Example
Linear Regulator
During operation of a prior art well known linear regulator such
as, for example, National LM317 (National Semiconductor, Santa
Clara, Calif.) series pass transistor is turned on continuously and
the output voltage is determined through a voltage divider and a
feedback circuit. There is a significant heat dissipation load for
the transistor. Furthermore, as a result of the continuous "on"
state of the transistor, there is a constant background current
draw regardless of the load. When a load is connected, the
conversion efficiency is typically not more than 30% for a ten fold
change in voltage down conversion.
Example of Switching Regulator
In a switching regulator (e.g. National LM78S40), pulse width
modulation (PWM) is used to switch the input voltage through a high
speed transistor at an adjustable duty cycle. In contrast to a
linear regulator where the series pass transistor is always on, in
a switching regulator the series pass transistor is turned on and
off at a convenient predetermined frequency (usually in the range
of about 25-250 kHz). The output voltage is the average of the
rectangular pulses resulting from such switching. Switching
regulation results in higher efficiency, such as over 30% and can
be as high as about 95%. In addition, the quiescent current draw is
also very low, typically less than 1 mA thus keeping overall heat
dissipation low. Additionally in some switching regulators, e.g.,
Maxim MAX 1627 (Maxim Company, Sunnyvale, Calif.), the quiescent
current draw can be further lowered to 1 .mu.A.
As shown in FIG. 37A, a switching regulator circuit used in this
invention can be based on a National LM78S40 switching regulator
chip U1. It accepts a 12V pre-regulated input voltage. A peak
current of 1.5A is assumed for this regulator. A sense resistor
calculated as 0.33/peak current according to the manufacturer, R4
detects the peak incoming current. Based on the value of input and
output voltage expected, a duty cycle of 23% is obtained. Assuming
a switching frequency of 25 kHz, a turn-on time of 33 .mu.s is
calculated. Based on the turn off time, the timing capacitor C2 of
0.15 .mu.F is then used to set the switching frequency to 25 kHz.
An inductor, L1 was used to couple the switching pulses while the
capacitor C1 reduces the ripples in the pulses to an average
voltage output. The combination of peak current and turn-on time
results in an inductance of 50 .mu.H. Voltage ripple of 1% is
tolerated resulting in the capacitor C1 of about 1 mF. The chip
contains a built-in PWM module, Darlington series pass transistor
and reference voltage. Trimmer resistor, R5, in conjunction with
series resistor R3, then sets the output voltage. The built-in
reference voltage is set at 1.3V which is the lower limit for the
regulated voltage. In the circuit the reference voltage is reduced
by using a voltage divider via series resistors, R1 and R2 of 1
M.OMEGA. each to further lower the minimum voltage regulated to
0.65V.
To change the applied potential to an EC device with temperature,
an NTC thermistor can also be used in place of trimmer resistor R5.
At higher temperatures, the resistance decreases, leading to lower
coloring and bleaching voltages while at lower temperatures, the
resistance is higher resulting in higher voltages.
Switching regulator radiates EMI due to the switching transistor.
Adequate shielding, e.g. Faradaic shield, must be provided to
mitigate such EMI to reduce electromagnetic interference with other
subsystems including communications such as a cellular phone. For
example the shielding aspect could be useful for powering of EC
components in a car or any other transportation vehicle. It is also
novel to use switching and linear regulator with the former working
when the car is in a parked state while the latter being used while
the car is parked (ignition off), the degree of interference to
other electronic systems is lower.
Example of a Switching Regulator with Ultra Low Quiescent Switching
Current
A switching regulator used in this invention employing a MAXIM Max
1627 yielding very low quiescent current of 0.001 mA is shown in
FIG. 37C. The switching efficiency is a high as 85% at 1A current
draw. Without modification using the manufacturers' specification,
this chip outputs voltage at a lower limit of 1.27V. In this
particular example, the circuit is modified, to allow output
voltages lower than 1.27V, by having feedback resistors R2 and R1
connected through a high speed comparator MAXIM Max 987. The
p-MOSFET used in the circuit was International Rectifier (El
Segundo, Calif.) IRF7416.
Example of Ramped Voltage Application
The voltage applied to the EC cell may consist of a non-linear
ramp. The ramp only refers to the time period when the voltage is
changing before the voltage settles at the hold potential (e.g.,
V.sub.C is holding potential in FIG. 38B). Such non-linearity can
be obtained, e.g., by having some amount of internal resistance in
the power supply. This internal resistance can be intentionally
designed into the power supply itself or by inserting an external
resistor between the voltage terminal and the EC cell. This is
shown in FIG. 38A where resistor R7 is placed in series with the
power supply output and EC cell. FIG. 38C describes the various
shapes that the voltage vs. time curves can follow depending on the
circuit parameters. The applied voltage is across the EC cell and
the resistor. During bleaching or coloring times, there will be a
large initial surge of current resulting in a sizable ohmic drop in
R7 which then limits the voltage applied to the EC cell. At
saturation, only a very low amount of current flows, and the
voltage drop across R7 becomes negligible and hence the EC cell
sees the full potential again. The overall voltage applied to the
EC cell during coloring and bleaching processes appears similar to
a capacitor charging curve. The sharpness of the curves depends on
the value of resistor used; larger resistance results in more
gradual and slower saturation.
Switching Power Supply where Output Voltage Varies with
Temperature
A switching regulator circuit was constructed similar to the one
described previously except that a thermistor was located in place
of fixed resistor R5--see FIG. 37B. An example of the thermistor
used is KE D331BZ from Thermometrics (Edison, N.J.). It exhibits
resistance values of 4000 .OMEGA. and 60 .OMEGA. at -25.degree. C.
and 65.degree. C. respectively. By having another fixed resistor R6
with a value of 3.6 k.OMEGA. in series with thermistor R5 and fixed
resistor R3 with a value of 5.6 k.OMEGA., the voltage was
automatically tuned to 1.3 V and 1 V at -25.degree. C. and
65.degree. C. respectively.
Other variations and modifications of this invention will be
obvious to those skilled in the art. This invention is not limited
except as set forth in the following claims.
* * * * *